Improve a test exception message.
Improve a test exception message.

* subversion/tests/cmdline/changelist_tests.py
  (verify_pget_output): If this fails, tell what we got and what we expected.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1103753 13f79535-47bb-0310-9956-ffa450edef68

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