dvdnav: improve title scanning

dvdnav: improve title scanning
- looks for ptt with longest pgc sequence instead of just picking first ptt
    solves many 'short title' problems
- constructs chapters from the pg's within the pgc's instead of using ptt's
    solve the problem of ptt's that point to an intro pgc instead of
    to the actual chapter position in the title.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@2361 b64f7644-9d1e-0410-96f1-a4d463321fa5