[PATCH] Issue 1199: Delete from multiple repos at one time

Attached is a patch for issue 1199:
http://subversion.tigris.org/issues/show_bug.cgi?id=1199

In spite of the 'bite-sized' keyword, this patch took a fair amount of
work, and I'm not yet certain that it is ready for commit, so I'm
sending it here for review first. The questions I have are:
 * The notification is still very sparse, and doesn't say what was
actually committed. For single URL rm, that's not an issue, but here
it is. Suggestions on how to improve the output welcomed (but I don't
want this to hold up the patch).
 * I don't know if this added issue 3242-like problems. The approach
is to parent the session at the repos_root, and then operate on all
the paths relative to that. In theory, I don't think this should be a
problem. In practice, I'm not so sure.

Other questions/comments/concerns are of course welcomed, but I'd like
to get this committed sooner, rather than later.

Thanks,
-Hyrum

[[[
Fix issue 1199: Make 'svn rm URL1 URL2 URL3' work, even if the URLs are from
different repositories.

* subversion/tests/cmdline/basic_tests.py
  (test_list): Make the basic_rm_urls_multi_repos test pass.

* subversion/libsvn_client/delete.c
  (delete_urls): Remove.
  (single_repos_delete): New.
  (delete_urls_multi_repos): New.
  (svn_client_delete4): Call delete_urls_multi_repos(), instead of the old
    function.
]]]