Playback of a DVD as files in a folder should not create a playlist

See discussion here:
https://github.com/xbmc/xbmc/pull/2855#issuecomment-28204668
and here:
http://forum.xbmc.org/showthread.php?tid=176066&pid=1547884#pid1547884

The issue at hand is that choosing PLAY on a DVD folder creates a playlist of the items in that folder instead of just playing the DVD. This causes the dvd to be played several times plus the chapters prev/next don't work correctly, since after #2855 playlist prev/next takes precedence if there's more than one item in the playlist...

Easiest solution was to only add the VIDEO_TS.IFO file to the playlist in this situation.