otherwise breaks PCR update on seek

Was regression with that tricky one:
http://streams.videolan.org/issues/10981/6.mp4

things that does not belong to libmp4

Adds a data order driven demuxer instead of trying
to rearrange seek order. Re-enables fragmented
files if fast-seekable.

So we can stop probing at some point.

wrong fix was 198bb199

signedness problems due to error handling

Fixes the false positive and fallback on avcodec with
files having a mvex/trex but no fragments, and conforms
to the spec.

ret cannot be NULL.

read spec and throw dice

and stop casting signed into unsigned (><)

John Stebbins authored Apr 09, 2014 and François Cartegnie committed Apr 13, 2014

Signed-off-by: Francois Cartegnie <fcvlcdev@free.fr>