UpdateSongPositions

It is useful to have Player SongPositions update off of ScreenGameplay
for use with things like ArrowEffects.

ScreenGameplay, ScreenHowToPlay, and ScreenEdit stop GameSoundManager
from running GameState:UpdateSongPosition and do it themselves, so this
has no impact on the screen classes that cared about, and thus updated,
player SongPositions.

src/ScreenHowToPlay.cpp

@@ -251,7 +251,7 @@ void ScreenHowToPlay::Update( float fDelta )
 	if( GAMESTATE->m_pCurSong != NULL )
 	{
 		RageTimer tm;
-		GAMESTATE->UpdateSongPosition( m_fFakeSecondsIntoSong, GAMESTATE->m_pCurSong->m_SongTiming, tm, true );
+		GAMESTATE->UpdateSongPosition( m_fFakeSecondsIntoSong, GAMESTATE->m_pCurSong->m_SongTiming, tm );
 		m_fFakeSecondsIntoSong += fDelta;
 
 		static int iLastNoteRowCounted = 0;