Bug 1066982 - Try to not launch processes on pre-JB devices because of Android bug. r=snorp, a=lmandel

On pre-JB Android, there's a bug in Bionic's fork implementation that can cause
a hang when launching processes, so this patch makes us avoid doing that if we can.
Bug 1080755 - Push video frames into MediaStreamGraph instead of waiting for pulls. r=padenot, a=lmandel