Merge branch 'stable-5.0' into stable-5.1

* stable-5.0:
  Fix NoSuchFileException during directory cleanup in RefDirectory
  Externalize warning message in RefDirectory.delete()
  Suppress warning for trying to delete non-empty directory

Change-Id: I9371f354d685545cc6a268420e44ae4c9577680f
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>