Make ra serf pipeline lock and unlock requests. Currently it does
this on a single connection, so performance can probably
be improved further.

* subversion/libsvn_ra_serf/lock.c
  (includes): Add assert.h and svn_sorts.h
  (lock_ctx_t: Add unlock members.
  (determine_error): Remove function.
  (run_locks): New function.

  (handle_lock): Always parse headers. Handle error 405.
  (svn_ra_serf__lock): Create all requests and then call run_locks.
     Set no_fail_on_http_failure_status.

  (set_unlock_headers): Use other baton type.
  (svn_ra_serf__unlock): Create all requests and then call run_locks.
     Set no_fail_on_http_failure_status.

* subversion/libsvn_ra_serf/ra_serf.h
  (svn_ra_serf__handler_t): Add boolean.

* subversion/libsvn_ra_serf/util.c
  (handle_response): Replace specialized lock handling with a boolean that
    allows response handlers to handle all errors themselves.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1551993 13f79535-47bb-0310-9956-ffa450edef68