Tweak the obstruction detection helper code for merging a bit to remove
some unused arguments and to avoid an additional call for shallowness tests.

* subversion/include/private/svn_wc_private.h
  (svn_wc__check_for_obstructions): Add two arguments.

* subversion/libsvn_client/merge.c
  (perform_obstruction_check): Add two arguments and remove another one.
  (merge_file_opened,
   merge_dir_opened,
   record_skips_in_mergeinfo): Update caller.

* subversion/libsvn_wc/node.c
  (svn_wc__check_for_obstructions): Fill a few more optional arguments.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1443248 13f79535-47bb-0310-9956-ffa450edef68