In the test suite, create and use an 'AlternateOutput' matcher class that
matches any of the given expected outputs.

* subversion/tests/cmdline/svntest/verify.py
  (AlternateOutput): New class.

* subversion/tests/cmdline/tree_conflict_tests.py
  (ensure_tree_conflict): Use it to strengthen the checks.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1449156 13f79535-47bb-0310-9956-ffa450edef68