pulsesrc: add support for renegotiation

Submitted by Sjoerd Simons @sjoerd

Link to original bug (#683902)

Description

Just after renegotiation started a lot of warnings are logged (which are probably harmless), unfortunately afterwards pa_stream_connect_record apparently fails.

0:00:06.580594086 1317 0x2ab7770 WARN audiosrc gstaudiosrc.c:245:audioringbuffer_thread_func:<pulsesrc0> error reading data -1 (reason: Success), skipping segment
0:00:06.580608406 1317 0x2ab7770 WARN audiosrc gstaudiosrc.c:245:audioringbuffer_thread_func:<pulsesrc0> error reading data -1 (reason: Success), skipping segment
0:00:06.580622683 1317 0x2ab7770 WARN audiosrc gstaudiosrc.c:245:audioringbuffer_thread_func:<pulsesrc0> error reading data -1 (reason: Success), skipping segment
0:00:06.580664593 1317 0x2ab7770 WARN audiosrc gstaudiosrc.c:245:audioringbuffer_thread_func:<pulsesrc0> error reading data -1 (reason: Success), skipping segment
0:00:06.580678688 1317 0x2ab7770 ERROR ringbuffer gstaudioringbuffer.c:1970:gst_audio_ring_buffer_set_timestamp:<audiosrcringbuffer0> Could not store timestamp, no timestamps buffer
0:00:06.580798741 1317 0x2ac91e0 INFO pulse pulsesrc.c:1407:gst_pulsesrc_prepare:<pulsesrc0> maxlength: -1
0:00:06.580818444 1317 0x2ac91e0 INFO pulse pulsesrc.c:1408:gst_pulsesrc_prepare:<pulsesrc0> tlength: -1
0:00:06.580832238 1317 0x2ac91e0 INFO pulse pulsesrc.c:1409:gst_pulsesrc_prepare:<pulsesrc0> prebuf: 0
0:00:06.580845753 1317 0x2ac91e0 INFO pulse pulsesrc.c:1410:gst_pulsesrc_prepare:<pulsesrc0> minreq: -1
0:00:06.580858797 1317 0x2ac91e0 INFO pulse pulsesrc.c:1411:gst_pulsesrc_prepare:<pulsesrc0> fragsize: 320
0:00:06.585881211 1317 0x2ac91e0 WARN pulse pulsesrc.c:1488:gst_pulsesrc_prepare:<pulsesrc0> error: Failed to connect stream: Invalid argument
empathy-Message: Element error: Failed to connect stream: Invalid argument -- pulsesrc.c(1488): gst_pulsesrc_prepare (): /GstPipeline:pipeline0/EmpathyGstAudioSrc:empathygstaudiosrc0/GstPulseSrc:pulsesrc0