Merge r1547774 from trunk:

 * r1547774
   Fix 'svn checkout ^/subversion/trunk NAS' of working copy with symlinks
   on Windows where the NAS doesn't implement FlushFileBuffers().
   Regression since 1.7.
   Justification:
     The checkout of symlink replacements shouldn't require more network
     capabilities than ordinary checkouts.
   Votes:
     +1: rhuijben, stefan2, steveking


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1561252 13f79535-47bb-0310-9956-ffa450edef68