Added Dancing Stage 3DDX (SINGLE MODE ONLY)

NOTE: I commented out an ASSERT in NoteData.cpp
at Line 429
//	ASSERT( iOriginalTrack < pOriginal->m_iNumTracks );
I don't understand how the AutoGen code works, but all I do know is
that the game works without this assert, but possibly in a way people
didn't want defined. Please can somebody (preferably Chris as he
says he's the only one who understands notedata :D) look at this
and figure out what i'm doing wrong.
I feel a bit uneasy taking out an assert to make things work....

stepmania/src/ScreenEz2SelectMusic.cpp

@@ -145,6 +145,14 @@ void ScreenEz2SelectMusic::MenuLeft( PlayerNumber pn, const InputEventType type
 
 void ScreenEz2SelectMusic::MenuStart( PlayerNumber pn )
 {
+	if( !m_MusicBannerWheel.GetSelectedSong()->HasMusic() )
+	{
+		/* TODO: gray these out. 
+			*
+			* XXX: also, make sure they're not selected by roulette */
+		SCREENMAN->Prompt( SM_None, "ERROR:\n \nThis song does not have a music file\n and cannot be played." );
+		return;
+	}
 	MUSIC->Stop();
 	SCREENMAN->SetNewScreen( "ScreenStage" );
 }