Revision 1914650

Add a second test for the mailer.py script, using revisions from
Apache Subversion itself, rather than mocked up revisions.

* subversion/tools/hook-scripts/mailer/tests:
  (svn:ignore): ignore some artifacts from the t1 and t2 tests
* subversion/tools/hook-scripts/mailer/tests/mailer-t2.sh:
  (..): new. fetch a set of dumpfiles for various revisions-of-interest
    from the primary repository. Use these to construct some local
    repositories. Run the mailer script on the revisions, and compare
    the result against the reference/expected result.
* subversion/tools/hook-scripts/mailer/tests/t2-reference:
  (..): new. expected mailer output for each revision-of-interest