Add new XFail regression test for a case where 'svn diff' triggers an
assertion.

Found by: stsp

* subversion/tests/cmdline/diff_tests.py
  (diff_deleted_in_move_against_repos): New XFail test.
  (test_list): Add diff_deleted_in_move_against_repos.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1605810 13f79535-47bb-0310-9956-ffa450edef68