mux: eliminate 32 track limit

The limit was due to using an uint32_t as a bit vector.  This solves 
the limitation by introducing an hb_bitvec_t struct for bit vectors
of unlimited size.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6181 b64f7644-9d1e-0410-96f1-a4d463321fa5