On the 'reparentless' branch: Add reparentless commit.

* subversion/include/svn_ra.h
  (svn_ra_get_commit_editor4): Bump version, add repos_relpath, and update
   description.
  (svn_ra_get_commit_editor3): Deprecate.
* subversion/libsvn_ra/deprecated.c
  (svn_ra_get_commit_editor3): Implement compat func.
* subversion/libsvn_ra/ra_loader.c
  (svn_ra_get_commit_editor4): Add repos_relpath.
* subversion/libsvn_ra/editor.c
  (svn_ra__use_commit_shim): Implement using compat API - we'll figure out a
   better solution later, but for now, I'm not going to touch this code. There
   is not tests...

* subversion/libsvn_ra/ra_loader.h,
  subversion/libsvn_ra_serf/ra_serf.h
  subversion/libsvn_ra_local/ra_plugin.c,
  subversion/libsvn_ra_serf/commit.c,
  subversion/libsvn_ra_svn/client.c
  (svn_ra__vtable_t::get_commit_editor,
   svn_ra_local__get_commit_editor,
   svn_ra_serf__get_commit_editor
   ra_svn_commit): Add repos_relpath.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/reparentless@1937890 13f79535-47bb-0310-9956-ffa450edef68