Extend the test handling locks with expiration dates.

* subversion/tests/cmdline/lock_tests.py
  (dav_lock_timeout): Extend and run for all RA layers.

* build.conf
  (lock-helper): New.
  (__ALL_TESTS__): Add lock-helper.

* subversion/tests/cmdline/lock-helper.c: New.

* subversion/tests/cmdline/svntest/main.py
  (lock_helper_binary, run_lock_helper): New.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1579606 13f79535-47bb-0310-9956-ffa450edef68