Add a test for 'svn diff --old X --new Y', where X and Y are working copies.
Add a test for 'svn diff --old X --new Y', where X and Y are working copies.

* subversion/tests/cmdline/diff_tests.py
  (make_diff_header): Add optional SRC_LABEL and DST_LABEL arguments.
   These are required to produce a good diff header for --old --new mode.
  (diff_two_working_copies, test_list): New test.

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