On the 'move-tracking-2' branch: Allow svnmover's 'put' command to
overwrite an existing file, like 'svnmucc put' can.

* subversion/svnmover/svnmover.c
  (execute): Remove the assertion that said the 'put' target must not exist.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/move-tracking-2@1638233 13f79535-47bb-0310-9956-ffa450edef68