Disallow some ambiguous command line invocations.

* subversion/svn/mergeinfo-cmd.c
  (svn_cl__mergeinfo): Error out if users try to use --revision, -R,
    or --depth when not in --show-revs mode.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1467006 13f79535-47bb-0310-9956-ffa450edef68