New CLI -  riak-admin handoff limit <action> <value>

 * Flag `--node` will operate on the given node
 * Without passing `--node` all nodes operated upon
 * `riak-admin handoff` lists subcommmands (limit only for now)
 * `riak-admin handoff limit` shows usage for limit subcommand
 * Add rpc versions of `riak-admin handoff limit --show` when using
   --force-rpc option.
Fix comment formatting (double-% FTW)
Merge pull request #640 from basho/feature/dtr/handoff-new-cli-1237

New CLI -  riak-admin handoff limit

Reviewed-by: macintux