On the log-message-templates branch, fix a crash.

* subversion/svn/copy-cmd.c
  (svn_cl__copy): Fully convert this function to use log_msg_func4.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-message-templates@1622701 13f79535-47bb-0310-9956-ffa450edef68