Following up on r1441186, reinstate the old header per merge-child behavior
for ancestrical merges.

* subversion/libsvn_client/merge.c
  (mark_dir_edited,
   mark_file_edited): Call notify_merge_begin before producing skip.

  (find_nearest_ancestor): Go through the list backwards to allow directly
    returning when we have the best match.

  (notify_merge_begin): Don't set the notified_merge_begin variable in the
    case when we detect different targets based on the mergeinfo children.

    Reverse some variables to implement a quick exit without allocating
    when we don't have a new start.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1441232 13f79535-47bb-0310-9956-ffa450edef68