Render property conflicts with diff3.

Thread: http://mail-archives.apache.org/mod_mbox/subversion-dev/201405.mbox/%3C20140506110855.GA1948@tarsus.local2%3E

* subversion/libsvn_wc/props.c
  (prop_conflict_from_skel): Always use INCOMING_BASE as the diff3 "older".
    Add detailed comment.

* subversion/tests/cmdline/merge_tests.py
  (simple_property_merges):
* subversion/tests/cmdline/move_tests.py
  (property_merge):
* subversion/tests/cmdline/prop_tests.py
  (prop_reject_grind):
    Update expectations.

* subversion/tests/cmdline/prop_tests.py
  (file_matching_dir_prop_reject):
    Add comment.  No functional change.



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595522 13f79535-47bb-0310-9956-ffa450edef68