This allows using pl_Yield() from video outputs and friends, on
condition that pl_Yield() return value be checked for NULLity.

Should fix #1667.

This should allow VLC to receive from PulseAudio RTP (untested)

Should fix a race condition about freed input usage.

This should fix some race condition of freed input usage.

Removed broken, unmaintained and unfinished code. May be restored after 0.9.0 if there is enough time to do this kind of stuff (should be merged with the Extended Controls panel anyway)