To reduce pulsing we now allow an arf just before forced key frames
and at the end of a clip or section (which may be stitched to
another clip or section). However, this does not make sense for
key frames arising from real scene cuts.
Change from original patch reflects other recent changes in regard
to alignment of gf/arf and kf groups.
Change-Id: I074a91d1207e9b3e28085af982f6718aa599775f
a00dad39bd