evil big commit (sorry):

Remove m_HoldNote array entirely.  Remove 2sAnd3s.  Store hold note
durations in the hold head.  hold_tail only still exists when InsertHoldTails
is used, to make SM parsing a little easier (may go away).  Add helpers
for iterating over ranges while including or excluding adjacent and overlapping
hold notes.  Range operations are now [start,end) instead of [start,end].
(probably more details coming to sm-dev soon)

stepmania/src/NotesWriterDWI.cpp

@@ -190,7 +190,6 @@ void NotesWriterDWI::WriteDWINotesField( RageFile &f, const Steps &out, int star
 {
 	NoteData notedata;
 	out.GetNoteData( notedata );
-	notedata.ConvertHoldNotesTo2sAnd3s();
 
 	const int iLastMeasure = int( notedata.GetLastBeat()/BEATS_PER_MEASURE );
 	for( int m=0; m<=iLastMeasure; m++ )	// foreach measure