Another automatic merge optimization.

* subversion/libsvn_client/merge.c:
  (find_last_merged_location): Limit the log range requested when finding
   the oldest eligible revision.

   

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1465677 13f79535-47bb-0310-9956-ffa450edef68