Allow to disable ssl on stomp.

As the $ssl_stomp_port is required to be a string and must be '\d+', i added a ssl_stomp to disable ssl on stomp protocol (erlang ssl library on debian wheezy is buggy)
The rebase is failing because we're now wrapping this in `if @ssl and @ssl_stomp_port`, does that meet your needs? Otherwise a rebase and fixing the typo above would get this in.