SetSavedToDisk in Save(), not in SM_SaveSuccessful. When we save the

whole file, all steps are saved to disk; we were only marking the
active steps.  This sequence would cause steps to be wrongly deleted:
 1: create easy and medium steps for one steps type; save
 2: on another steps type, edit easy steps which were autogenned from the above
        change the steps
 3: f6 to change to medium steps steps which were autogenned from the above
 4: menu -> save
        This will save all data, but only medium will be marked saved to disk.
 5: f5 to change back to easy steps
 6: menu -> exit
        This will delete the easy steps, because they were not marked saved to disk.

stepmania/src/ScreenEdit.cpp

@@ -2551,7 +2551,6 @@ void ScreenEdit::HandleScreenMessage( const ScreenMessage SM )
 	else if( SM == SM_SaveSuccessful )
 	{
 		LOG->Trace( "Save successful." );
-		m_pSteps->SetSavedToDisk( true );
 		CopyToLastSave();
 		SetDirty( false );
 		SONGMAN->Invalidate( GAMESTATE->m_pCurSong );
@@ -2806,6 +2805,8 @@ void ScreenEdit::HandleMainMenuChoice( MainMenuChoice c, const vector<int> &iAns
 							break;
 						}
 
+						m_pSteps->SetSavedToDisk( true );
+
 						// HACK: clear undo, so "exit" below knows we don't need to save.
 						// This only works because important non-steps data can't be changed in
 						// home mode (BPMs, stops).