When the merge code detects and installs a tree conflict, the single file
merge notification handling shouldn't tell that we just skipped the file.

* subversion/libsvn_client/merge.c
  (single_file_merge_notify): Don't accidentally overwrite a tree conflict.

* subversion/tests/cmdline/merge_tests.py
  (merge_target_selection): Update expected result.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1440037 13f79535-47bb-0310-9956-ffa450edef68