mux: fix problems created by >32 track limit patch

First problem was pre-existing, but hidden.  Interleaving was severely
broken because we relied on buf->s.stop to determin interleave points.
stop is not guaranteed to be set.

Other problems with the new bit vector code caused failure to complete
muxing.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6187 b64f7644-9d1e-0410-96f1-a4d463321fa5