Two semi-related changes: tweak the stack traces, again, and rely on that tweak
to make it easier for the Python tests to recognise the new format.

* subversion/libsvn_subr/error.c
  (print_error): Add a comma at the end of bare file:lineno lines.

* subversion/tests/cmdline/merge_automatic_tests.py
  (subtree_to_and_fro),
* subversion/tests/cmdline/merge_reintegrate_tests.py
  (run_reintegrate_expect_error),
* subversion/tests/cmdline/merge_tests.py
  (merge_with_os_deleted_subtrees):
    Factor out common code into...

* subversion/tests/cmdline/svntest/main.py
  (stack_trace_regexp): .. this new module-global.  In addition, extend the
    regular expression to catch the bare file:lineno lines.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1467481 13f79535-47bb-0310-9956-ffa450edef68