Fix FrameConfigs used for VP8 with four temporal layers.
sync flag should only be true if:
* temporal layer > 0
* frame predics _only_ from tl0 (last)
Furthermore, flags should not predict from a buffer unless it has been
previously updated in the current iteration for the pattern.
I also added an experiment with an alternative pattern for a three
layer setup, where loose some efficieny by halving the pattern but
gain a little bit by updating arf for the top layer. The theory is that
this will cause fewer frame drops since we don't have as much
dependency on previous frames in the upper layer (which might not be
6 files changed