Add a missed test condition to diff_tests 31 that the current implementation doesn't quite pass.
Add a missed test condition to diff_tests 31 that the current
implementation doesn't quite pass.

* subversion/tests/cmdline/diff_tests.py
  (diff_prop_change_local_propmod): Test for properties that only exist
    locally in addition to properties that exist in all three locations
    (i.e. repos, BASE, WORKING).
  (test_list): Mark diff_prop_change_local_propmod as XFail.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion