The condition for waking up the V4L2 thread is not good. mblk_t become free when the last filter in the chain no longer uses them.
Furthermore the signal() was done only at fps rate in process method, which was not sufficient.
In order to prevent busy loop in case all buffers are used, an usleep() was added.

Conflicts:
	src/voip/audiostream.c

Conflicts:
	include/mediastreamer2/bitratecontrol.h
	src/voip/bitratecontrol.c
	src/voip/mediastream.c
	src/voip/qosanalyzer.c
	src/voip/videostream.c

add on_action_suggested callback for qos analyser which receive input and output (decision) of the algorithm

Conflicts:
	src/videofilters/vp8.c
	tester/Makefile.am
	tester/mediastreamer2_audio_stream_tester.c
	tester/mediastreamer2_tester.c
	tester/mediastreamer2_tester.h

Prefer native over compressed over emulated as long as FPS for requested
resolution is >= 15 images/sec.

But use avcodec_alloc_frame()/avcodec_free_frame()
See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=699722 for reference.

If a device is capable of YUYV non-emulated format and
YUV420P emulated (cpu color conversion), then pick the
non emulated one.
In the worst case (encoder with no YUYV support), pixconv
will be used to convert YUYV -> YUV420P.
In the best case (encoder supports YUYV input), we skip a
costly color-conversion step.

Allow these filter to specify if they support non-YUV420P
format (e.g: YUYV). If true, feed them with this format instead
of using pixconv.