Return "501 Not Implemented" rather than "401 Unathorized" when
anonymous LOCK requests fail.  Return "412 Precondition Failed"
rather than "401 Unathorized" when a LOCK refresh has the wrong
token.  The 401 responses were not valid HTTP.  Fixes part of
issue 4368.

* subversion/mod_dav_svn/lock.c
  (append_locks, remove_lock): Return 501.
  (refresh_locks): Return 501 or 412.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1489339 13f79535-47bb-0310-9956-ffa450edef68