interface should be done pretty soon (i'll try to finish it tomorrow)

 vlm.html : vlm web interface. What works: sending broadcast and vod creation
            commands

 js/vlm.js : add code to handle sending vlm commands.

 requests/vlm_cmd.xml : used to send a vlm command and get the resulting
                        error message

 requests/vlm.xml : export the full vlm media/schedules "tree". I still need
                    to parse that in js/vlm.js in order to display it in
                    dialogs/vlm .

 dialogs/* : dialogs' code which is used as building blocks for the
             main pages. (in order to avoid code duplication)

 mosaic.html, js/mosaic.js, dialogs/mosaic : start of a mosaic help
            page. nothing works and it's almost empty but i didn't feel like
            sorting through the commited files.

Since vlm commands are often full of spaces, you need to use the ";"
command delimiter to mark the end of a command.

For example : <vlc id="rpn" param1="; broadcast name new vlm_cmd" />

  Grmbl @ Digidesign coders...

    paved the way for private SPU commands.

Add a PLAYLIST_PREPARSE flag to tell that the item must be enqueued for preparse on add (not implemented yet).

Refs:#192

dshow.cpp: Removed default preferred media types (I420) as it was reported by Paul Sokolovsky to cause kernel crashes
           with some buggy drivers. I added these media types a while back to get around another bug for drivers that
           didn't offer any preferred media types.
           Hopefully, the latter bug should be indirectly fixed when I added support for IAMStreamConfig.
           Moreover, I modified the selection of a default format in IAMStreamConfig to take
           GetFourCCPriority into a account.