Still send silence when we are not doing anything else, but also flush the buffers...

Still send silence when we are not doing anything else, but also flush the buffers correctly upon recovery from suspension.

Close the RTP socket correctly after passing messages about.
When not sending silence, the RTSP socket will be closed after some period of inactivity. I'm not sure why this is.
Sending silence keeps things working and with the flushes after suspension we now get a better latency. As this relies on the auto-suspend feature, it's not exactly ideal.
Typical latencies are currently about 3s which makes it more or less usuable for listening to music.
If the connection is disconnected, it will reconnect but I've found that the second connection is silent. Hopefully the silence will prevent the first connection dropping.
Refs #69

git-svn-id: file:///home/lennart/svn/public/pulseaudio/branches/coling@2504 fefdeb5f-60dc-0310-8127-8f9354f1896f