Add regression test for issue
Found by: Mikhail Veltishchev <dichlofos-mv{_AT_}yandex.ru>
which applies to both trunk and 1.8.x

* subversion/tests/cmdline/diff_tests.py
  (diff_parent_dir): New test, marked XFail because it triggers an assertion.
  (test_list): Add new test.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1604736 13f79535-47bb-0310-9956-ffa450edef68