libavsmash: Trust formatSpecificFlags for 'lpcm'.
utils: Improve NTSC timebase detection.
lwlibav_video: Handle VP8 and VP9 invisible frame.
lwlibav_video: Fix DTS-based avg. fps calculation introduced at the previous commit.
lwindex: Exclude an incomplete pair of field coded picture from the repeat control.
all: Remove LSMASH_DEMUXER_ENABLED.

Require L-SMASH rev1323 or newer.
lwlibv_video: Fix handling of the last frame when counterpart of a pair of field coded pictures is missing.