Follow-up to r26945, move Win path '\' regexp escaping code to common helper.
Follow-up to r26945, move Win path '\' regexp escaping code to common helper.

* subversion/tests/cmdline/merge_tests.py
  (expected_merge_output): Construct correct regular expressions on Windows
  where paths may contain '\'s.
  (merge_fails_if_subtree_is_deleted_on_src): Revert r26945.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion