Fix unnecessary sleeping after a copy or move, following r1463721.

In r1463721, I stopped passing a specific path to the sleep function,
which meant it could no longer choose a sleep appropriate to the
file system and so might sleep longer than necessary; and I also
failed to initialize the 'sleep required' flag to false, which meant it
might sleep even after copying to a URL.

* subversion/libsvn_client/copy.c
  (try_copy): Document the 'timestamp_sleep' parameter.
  (svn_client_copy6, svn_client_move7): Initialize the flag.
    Pass the destination path to the sleep function.

Found by: philip
          me

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1466876 13f79535-47bb-0310-9956-ffa450edef68