Merge remote-tracking branch 'ffmpeg-mt/master'

    * ffmpeg-mt/master:
      Update todo.
      h264: add an assert that copied pictures are valid picture pointers
      valgrind-check: run with 1 and 3 threads
      h264: When decoding a packet with multiple PPS/SPS, don't start the next thread until all of them have been read
      Allow some pictures to be released earlier after 51ead6d2c40c5defdd211f435aec49b19f5f6a18
      h264: fix slice threading MC reading uninitialized frame edges.

    Please see ffmpeg-mt for a list of authors of these changes.

    Conflicts:
        libavcodec/h264.c
        mt-work/valgrind-check.sh

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>