PulseAudio plugin: report XRUN state back to application

PulseAudio plugin: report XRUN state back to application

From: Lennart Poettering <mznyfn@0pointer.de>

It adds support to report back XRUN to the application if one
happens. This is required to make some applications work on top of the
pulse plugin. One being XMMS, which checks if a song finished to play
by waiting for an XRUN (yes, I don't argue that XMMS shouldn't do
that, but nonetheless it is a good thing if XRUNs are reported
properly.)