Following up on recent server error processing improvements in libsvn_ra_serf
remove more client side error message generation. The server generated error
just tells us if the administrator should install a hook.

* subversion/libsvn_ra_serf/commit.c
  (maybe_set_lock_token_header): Filter the root relpath, as we only support
    locks on files there will never be one.
  (setup_proppatch_headers): Don't call maybe_set_lock_token_header if we don't
    have a path.
  (proppatch_resource): Patch error code to give API users some hints to avoid
    having to wrap with now unneeded information in...
  (svn_ra_serf__change_rev_prop): ... this function.

* subversion/tests/cmdline/prop_tests.py
  (post_revprop_change_hook): Assume more detailed error code.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1553484 13f79535-47bb-0310-9956-ffa450edef68