change semantics of SwfdecBits.idx handling
change semantics of SwfdecBits.idx handling

previously functions reading whole bytes called swfdec_bits_syncbits before
doing any reading. Now everyone using SwfdecBits for reading bits is
responsible for syncing when they want to resume reading bytes. The byte
reading code asserts that bits->idx == 0.

This change may introduce segfaults with code that isn't yet canged to call
swfdec_bits_syncbits() manually.

freedesktop-unofficial-mirror/swfdec__swfdec,mltframework/swfdec,freedesktop-unofficial-mirror/swfdec__swfdec,mltframework/swfdec,freedesktop-unofficial-mirror/swfdec__swfdec