Merge r1488267 from trunk:

 * r1488267
   Fix issue #4370 '(m)erge interactive conflict resolution segfaults when cwd
   not parent of target'.
   Justification:
     Prevents a segfault in the new 'internal text conflict merge tool'.
   Votes:
     +1: pburba (for 1.8.0:  This isn't a 'destabilizing' change per my
                 reading of our release-stabilization guidelines, so it can
                 be included in 1.8.0 without a soak restart.)
     +1: rhuijben, danielsh


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1488642 13f79535-47bb-0310-9956-ffa450edef68