In the merge code: Use the batons to detect whether we are at the root of an
added tree, instead of doing hash table lookups.

* subversion/libsvn_client/merge.c
  (record_update_add): Remove unneeded code.
  (merge_file_added,
   merge_dir_added): Record the roots of added trees.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1442372 13f79535-47bb-0310-9956-ffa450edef68