Implement GlobalOffsetSeconds in GameState::UpdateSongPosition,

not TimingData.  TimingData is a simple data structure, and shouldn't
be affected by hardware tweaks.  This is also easier to bypass in cases
we don't want GlobalOffsetSeconds.

Don't adjust assist tick by GlobalOffsetSeconds.

stepmania/src/GameState.cpp

@@ -582,6 +582,7 @@ const float GameState::MUSIC_SECONDS_INVALID = -5000.0f;
 void GameState::ResetMusicStatistics()
 {	
 	m_fMusicSeconds = 0; // MUSIC_SECONDS_INVALID;
+	m_fMusicSecondsNoOffset = 0;
 	m_fSongBeat = 0;
 	m_fCurBPS = 10;
 	m_bFreeze = false;
@@ -643,6 +644,10 @@ void GameState::ResetStageStatistics()
 
 void GameState::UpdateSongPosition( float fPositionSeconds, const TimingData &timing, const RageTimer &timestamp )
 {
+	m_fMusicSecondsNoOffset = fPositionSeconds;
+
+	fPositionSeconds += PREFSMAN->m_fGlobalOffsetSeconds;
+
 	if( !timestamp.IsZero() )
 		m_LastBeatUpdate = timestamp;
 	else