Support extenal .sup subtitles from Blu-ray-movies

As requested in: http://forum.videolan.org/viewtopic.php?f=7&t=51455&start=100#p317117

VLC 1.2.x can play .sup subtitles if they are in .m2ts files. But if those subtitles are in separate file, VLC cannot open them (unable to load subtitles from 'C:\00011.track_4622.sup').

Sample file for testing (unzip first): http://www.megaupload.com/?d=VP0DSGK6

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