Obtain realtime privileges using rtkit

[ewtoombs]

Summary

rtkit is a daemon that user processes can use to request and receive realtime privileges. It is how pulseaudio runs in realtime. Jack could use the same method.

Basic example

This new behaviour may be enabled using a boolean switch, like --rtkit.

Motivation

If jack obtained its realtime privileges using rtkit, then jack users would not need to go through the extra work they currently do just to get jack to run in realtime.