Fix issue 4369, poor serf error message for commit with stolen locks.

* subversion/libsvn_ra_serf/commit.c
  (maybe_set_lock_token_header): Associate URI with lock token.

* subversion/tests/cmdline/lock_tests.py
  (commit_stolen_lock): New regression test.
  (test_list): Add new test.

* subversion/tests/cmdline/svntest/sandbox.py
  (simple_lock): New.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1488425 13f79535-47bb-0310-9956-ffa450edef68