Originally, the AdjustSync class always saved to disk, even in edit mode.

In edit mode, though, AdjustSync should only save to memory, giving the
user a chance to save later.  This change adds a SongChanged message
to the MessageManager.  Making the ScreenEdit class listen to this
message allows the AdjustSync class to mark a song as dirty rather than
saving it to disk when in edit mode.

R=steve chekoway

stepmania/src/MessageManager.cpp

@@ -132,6 +132,7 @@ static const char *MessageNames[] = {
 	"ShowHoldJudgmentMuliPlayerP30",
 	"ShowHoldJudgmentMuliPlayerP31",
 	"ShowHoldJudgmentMuliPlayerP32",
+	"MessageSongChanged",
 };
 XToString( Message );