Follow-up to commit r15287 which caused a regression - (un)locking
multiple files over ra_svn fails for benign (un)locking errors.  Modified
the ra_svn protocol and implementation for (un)lock-many to return status
for each path on (un)lock. Minor style fixes for comments, declarations.

* subversion/libsvn_ra_svn/protocol: grammar change
  (lock-many): instead of returning a single response with multiple lock
  descriptions, return one lock description per path on success
  (unlock-many): instead of returning a single multi-path response,
  return each successfully unlocked pathname on success
* subversion/libsvn_ra_svn/client.c:
  (ra_svn_lock): accept multiple lock-many responses from server
  (ra_svn_unlock): accept multiple unlock-many responses from server
* subversion/svnserve/serve.c:
  (lock_many): Now returns multiple lock descriptions, one per path
  (unlock_many): Now returns multiple responses, one per path
* subversion/tests/clients/cmdline/lock_tests.py:
  (unlock_already_unlocked_files): New test
  (test_list): Added unlock_already_added_files