avformat: only perform global network init once.
pthread_lockmgr: use a recursive pthreads mutex

This allows locking the same mutex multiple times from the same thread,
which can happen easily in some situations.
matroskadec_haali: support V_PRORES
riff: add ProRes FourCCs
dcadsp: fix SSE code to not use SSE2 instructions.

movq from SSE register to memory is an SSE2 instruction.
Instead, use SSE movlps, which does the same thing.
avisynth: set duration of audio streams