Fix issue #4481 "automatic merge confused by missing subtree merge".

* subversion/libsvn_client/merge.c
  (find_unsynced_ranges): Fix typo in doc string.
  (find_reintegrate_merge): Pass the correct target path to
    find_unsynced_ranges: don't assume the target path is equal to the
    youngest common ancestor path.

* subversion/tests/cmdline/merge_automatic_tests.py
  (reintegrate_subtree_not_updated): Remove XFail. Tweak the expectations
    and comments.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1580867 13f79535-47bb-0310-9956-ffa450edef68