Further clean up the ExpectedOutput classes in the test suite.

* subversion/tests/cmdline/svntest/verify.py
  (ExpectedOutput, RegexOutput): Write proper doc strings. Give each class
    its own __init__() method. Override the matches() method instead of
    delegating to an is_equivalent_list() method.
  (UnorderedOutput): The same, and don't support the 'match_all=False' case
    as we don't need it.
  (UnorderedRegexOutput): The same, and don't use multiple inheritance as we
    don't need it.

* subversion/tests/cmdline/externals_tests.py
  (pinned_externals): Make the argument to RegexOutput() a string not a
    list, for consistency with everywhere else, as it's now enforced.

* subversion/tests/cmdline/changelist_tests.py
  (tree_conflicts_and_changelists_on_commit): Use RegexOutput instead of
    UnorderedRegexOutput because that's all we need and UnorderedRegexOutput
    no longer supports this 'match any' usage.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1443675 13f79535-47bb-0310-9956-ffa450edef68