Add a test for a part of issue #3121 that appears to be working now.

* subversion/tests/cmdline/prop_tests.py
  (peg_rev_base_working): New test.
  (test_list): Run it.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1454190 13f79535-47bb-0310-9956-ffa450edef68