demux: fix problem with widely spaced SCRs

Fixes this bug report https://forum.handbrake.fr/viewtopic.php?f=12&t=30032

Split MPEG demuxer into TS demuxer and PS demuxer to allow using different
PCR/SCR delta tolerance in each scenario.

We were using a PCR/SCR delta tolerance that was a bit of a compromise
between the max allowed by the specification for TS vs PS streams.  But
the spec for TS PCR is 100ms and the spec for PS SCR is 700ms, so we
risked false detection of discontinuities in PS.  In PS streams that pack
multiple frames into one PES packet, the detection of a discontinuity
causes recalculation of an scr offset which jumps around wildly.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6183 b64f7644-9d1e-0410-96f1-a4d463321fa5