Following up on r1433621, switch the added file handling in the merge code
to the wc-ng based obstruction handling.

* subversion/libsvn_client/merge.c
  (merge_file_added): Use perform_obstruction_check for obstruction and tree
    conflict checks.
  (merge_dir_added): Fix comment.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1433678 13f79535-47bb-0310-9956-ffa450edef68