Backport r1455352 onto 1.7.x:

 * r1455352
   Improve logic in mod_dav_svn's implementation of lock.
   Votes:
     +1: breser, philip, pburba



git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x@1462331 13f79535-47bb-0310-9956-ffa450edef68