Merge the r1584576 group from trunk:

 * r1584576, r1584592, r1584745
   Resolve issue #3515 "mod_dav_svn cannot refresh any locks"
   Justification:
     Without this patch generic DAV clients can not refresh their own locks,
     causing them to lose their locks.
   Notes:
     Patch needed, because a plain merge triggers a text conflict while
     removing the XFail marker from the test. r1584745 makes the test code
     compatible with 1.8.
   Votes:
     +1: rhuijben, philip, breser



git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1591134 13f79535-47bb-0310-9956-ffa450edef68