Partial fix for Issue #443: post-commit hook script (error) output lost
   Includes post-commit hook stderr propagation for ra_dav
   Does not include post-commit hook stderr propagation for ra_local and
   ra_svn.
   Does not include the pre-revprop-change fix.

   * subversion/libsvn_ra/ra_loader.c
     (svn_ra_find_protocol): New API to find out which schema/protocol
     would be used, given a URL.
     (svn_ra_get_commit_editor2): New version of the API to use
     the new commit_editor function and hence use the new callback.
   * subversion/libsvn_ra/ra_loader.h
     (svn_ra__vtable_t): Added comments for get_commit_editor and
     intoduced a new member get_commit_editor2 which now uses the
     svn_commit_callback2_t.
   * subversion/include/svn_repos.h
     (svn_repos_get_commit_editor3): New API to accomodate the
     svn_commit_callback2_t callback type.
   * subversion/include/svn_types.h
     (svn_commit_callback2_t): Ah, the core change. A callback that
     takes the post_commit_err parameter.
   * subversion/include/svn_client.h
     (svn_client_commit_info2_t): The structure that carries the
     commit success parameters now has to carry the post_commit_err too.
     (svn_client_mkdir): mkdir should now use the new structure -
     svn_client_commit_info2_t.
     (svn_client_delete): delete should now use the new structure -
     svn_client_commit_info2_t.
     (svn_client_commit3): New API that uses svn_client_commit_info2_t.
     (svn_client_copy2): New API that uses svn_client_commit_info2_t.
   * subversion/include/svn_ra.h
     (svn_ra_find_protocol): New API declaration added.
     (svn_ra_get_commit_editor2): New API that uses the new callback.
   * subversion/libsvn_ra_local/ra_plugin.c
     (ra_local_vtable): ra_local's vtable does NOT have callback2.
   * subversion/libsvn_client/delete.c
     (delete_urls): delete_urls now uses the svn_client_commit_info2_t
     structure.
     Call svn_ra_get_commit_editor2() if ra_dav.
     Call svn_ra_get_commit_editor() otherwise.
     (svn_client_delete): svn_client_delete should now use
     svn_client_commit_info2_t.
   * subversion/libsvn_client/client.h
     (svn_client__commit_get_baton): Should now use the new commit
     info structrure - svn_client_commit_info2_t.
     (svn_client__commit_callback2): New callback that now takes
     post_commit_err as one of its parameters.
   * subversion/libsvn_client/copy.c
     (repos_to_repos_copy): Now uses the svn_client_commit_info2_t
     structure.
     Call svn_ra_get_commit_editor2() if ra_dav.
     Call svn_ra_get_commit_editor() otherwise.
     (wc_to_repos_copy): Now uses the svn_client_commit_info2_t
     structure.
     Call svn_ra_get_commit_editor2() if ra_dav.
     Call svn_ra_get_commit_editor() otherwise.
     (setup_copy): Now uses svn_client_commit_info2_t.
     (svn_client_copy2): New version of API that takes a
     svn_client_commit_info2_t for commit_info.
     (svn_client_move3): New version of API that takes a
     svn_client_commit_info2_t for commit_info.
   * subversion/libsvn_client/commit_util.c
     (commit_baton): Now uses svn_client_commit_info2_t.
     (svn_client__commit_get_baton): Now uses svn_client_commit_info2_t.
     (svn_client__commit_callback2): This callback function
     fills the svn_client_commit_info2_t structure with the
     post_commit_err, if any.
   * subversion/libsvn_client/add.c
     (mkdir_urls): Now uses svn_client_commit_info2_t.
     Calls svn_ra_get_commit_editor2() if ra_dav.
     Calls svn_ra_get_commit_editor() otherwise.
     (svn_client_mkdir): Now uses svn_client_commit_info2_t.
   * subversion/libsvn_client/commit.c
     (get_ra_editor): Now uses svn_client_commit_info2_t.
     Calls svn_ra_get_commit_editor2() if ra_dav.
     Calls svn_ra_get_commit_editor() otherwise.
     (svn_client_import2): get_ra_editor now passed typecasted commit_info.
     (svn_client_commit3): New version of API that uses
     svn_client_commit_info2_t.
     (svn_client_commit2): A svn_client_commit_info2_t is allocated
     and passed back as svn_client_commit_info_t. This doesn't matter
     as svn_client_commit_info2_t is one member more than
     svn_client_commit_info_t.
   * subversion/mod_dav_svn/merge.c
     (#include): Included svn_xml.h
     (dav_svn__merge_response): Now takes an extra post_commit_err
     parameter. If the post_commit_err is available,
     - Adds the SVN namespace
     - post-commit-err element to hold the post_commit_err
        to the merge response.
   * subversion/mod_dav_svn/dav_svn.h
     (dav_svn__merge_response): Now takes a new post_commit_err
     parameter.
   * subversion/mod_dav_svn/version.c
     (dav_svn_merge): If post-commit hook returns an error,
     pass it along to dav_svn__merge_response.
   * subversion/clients/cmdline/cl.h
     (svn_cl__print_commit_info2): Declaration for the new function
     that ultimately prints out the post-commit hook's stderr to
     the user.
   * subversion/clients/cmdline/mkdir-cmd.c
     (svn_cl__mkdir): Now uses svn_client_commit_info2_t and
     svn_cl__print_commit_info2.
   * subversion/clients/cmdline/move-cmd.c
     (svn_cl__move): Now uses svn_client_commit_info2_t and
     svn_cl__print_commit_info2.
   * subversion/clients/cmdline/copy-cmd.c
     (svn_cl__copy): Now uses svn_client_commit_info2_t and
     svn_cl__print_commit_info2.
   * subversion/clients/cmdline/util.c
     (svn_cl__print_commit_info2): Home at last!!! New version of API.
     svn_cl__print_commit_info2 is the function that ultimately
     prints out the post_commit_error to the user.
   * subversion/clients/cmdline/commit-cmd.c
     (svn_cl__commit): Now uses svn_client_commit_info2_t and
     svn_cl__print_commit_info2 for callback.
   * subversion/clients/cmdline/delete-cmd.c
     (svn_cl__delete): Now uses svn_client_commit_info2_t and
     svn_cl__print_commit_info2 for callback.
   * subversion/tests/clients/cmdline/commit_tests.py
     (post_commit_hook_test): New function to test the post-commit
     hook's propogation of stderr to the client.
     (test_list): Added post_commit_hook_test to list of tests.
   * subversion/libsvn_repos/hooks.c
     (svn_repos__hooks_post_commit): Now runs the post-commit hook
     with the read_errstream parameter as TRUE.
   * subversion/libsvn_repos/commit.c
     (edit_baton): Added new member - callback2, to hold a callback of 
     type svn_commit_callback2_t. Also added comments that callback
     should be removed once all code uses callback2.
     (close_edit): Handles the post-commit stderr. Decides whether
     to use the callback or the callback2 member of the edit baton.
     (svn_repos_get_commit_editor3): Uses svn_commit_callback2_t for
     callback type, and fills callback2 of the edit baton.
     (svn_repos_get_commit_editor2): Still uses svn_commit_callback_t
     and fills the callback member of the edit baton.
   * subversion/libsvn_ra_svn/client.c
     (ra_svn_vtable): ra_svn's vtable doesnt have a get_commit_editor2
     member.
   * subversion/libsvn_ra_dav/merge.c
     (merge_elements): Added the post-commit-err element.
     (merge_ctx_t): Added the post_commit_err member.
     (validate_element): Make ELEM_post_commit_err a valid element.
     (end_element): Add case, and handle ELEM_post_commit_err.
     (svn_ra_dav__merge_activity2): New merge function to handle
     post-commit hook's stderr.
   * subversion/libsvn_ra_dav/ra_dav.h
     (svn_ra_dav__get_commit_editor2): New version of API, using
     svn_commit_callback2_t.
     (enum): Added ELEM_post_commit_err member.
     (svn_ra_dav__merge_activity2): Declaration for new version of API.
   * subversion/libsvn_ra_dav/session.c
     (dav_vtable): Now contains a get_commit_editor2 function, but no
     get_commit_editor function.
   * subversion/libsvn_ra_dav/commit.c
     (commit_ctx_t): Added the callback2 member.
     (commit_close_edit): Now uses te svn_ra_dav__merge_activity2
     function.
     (svn_ra_dav__get_commit_editor2): Now fills the callback2 member
     (svn_ra_dav__get_commit_editor): Still fills the callback member