Merge r1551579 from trunk:

This should have been part of r1565079, which backported r1551524.

 * r1551524, 1551579
   Fix an 'No Write Lock' error when moving files between externals and
   parent working copies or vice versa.
   Justification:
     svn move should just work in these cases.
   Votes:
     +1: rhuijben, stefan2, breser


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1567239 13f79535-47bb-0310-9956-ffa450edef68