libhb: re-enable vobsub in mp4 support


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6401 b64f7644-9d1e-0410-96f1-a4d463321fa5
contrib: bump dvdnav to 5.0.1 and dvdread to 5.0.0


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6402 b64f7644-9d1e-0410-96f1-a4d463321fa5
dvdnav: remove debug hack i used for testing


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6403 b64f7644-9d1e-0410-96f1-a4d463321fa5