Add daemontools support

At Mochi Media, we are starting Riak using 'riak console' instead of 'riak start', since daemontools doesn't work with background applications, and run_erl doesn't properly handle signals.

Also, we had to implement our own command "riak remsh", which is basically "erl -remsh".

* Add 'riak dt_start' command to be executed from daemontools run script.
* Extend 'riak attach' command to determine riak start mode and use
  "erl remsh" for daemontools-started node.

P.S. If this goes upstream, we'll finally be able to use 100% non-customized Riak :)