On the 'move-tracking-2' branch: Change 'svnmover' implementation to use
element-based addressing and make the 'merge' command apply and commit the
results of the merge (if there is no conflict).

* subversion/include/private/svn_editor3.h,
  subversion/libsvn_delta/editor3.c,
  subversion/libsvn_delta/compat3.c
  Implement element-based editor3_t API methods.
  Changes to public API:
  (svn_editor3_nbid_t): Change the type to 'int'.
  (svn_editor3_add): Return the new element id.
  (svn_editor3_instantiate): New.
  (svn_editor3_copy_one,
   svn_editor3_alter): Allow the new content to be null meaning unchanged.
  (svn_editor3__get_baton): Renamed from 'svn_editor3_get_baton'.
  (svn_editor3_node_content_dup): Implement.
  (svn_editor3_node_content_equal): New.
  (svn_branch_repos_t, svn_branch_repos_create,
   svn_branch_revision_root_t, svn_branch_revision_root_create
   svn_branch_family_t, svn_branch_family_create,
   svn_branch_sibling_t, svn_branch_sibling_create,
   svn_branch_instance_t, svn_branch_instance_create,
   svn_branch_el_rev_id_t,
   svn_branch_el_rev_content_t, svn_branch_el_rev_content_create,
   svn_branch_el_rev_content_equal,
   svn_branch_get_root_rrpath,
   svn_branch_get_rrpath_by_eid,
   svn_editor3_find_branch_element_by_rrpath,
   svn_editor3_find_el_rev_by_path_rev,
   svn_branch_revision_root_parse,
   svn_branch_revision_root_serialize,
   svn_branch_get_family,
   svn_branch_subtree_differences,
   svn_branch_branch,
   svn_branch_branchify,
   svn_delta__ev3_from_delta_for_commit2,
   ): New.

* subversion/libsvn_ra/ra_loader.c
  Load the branching info from the repository when getting a commit editor,
  and store the updated info when a commit succeeds.

* subversion/svnmover/svnmover.c
  Move much of the implementation of branching out of here.
  Switch to element-based editor methods.
  Make the 'merge' command apply and commit the results of the merge (if
  there is no conflict).
  Remove the "-b [--branch]" option and choose a branch based on the path
  arguments instead.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/move-tracking-2@1634591 13f79535-47bb-0310-9956-ffa450edef68