significantly improve chart preview sync for mp3 files

default "accuratesync" to true when loading mp3s
i dont know why it's defaulted to false and i don't know why it exists in the first place

seeking still causes mp3 files to desync slightly (but not ogg???) however it's still a vast improvement

seeking can be done without desync by completely starting the music anew however this causes about a quarter second delay and isn't worth it, my guess is the desync has to do with the fact that the sound position is being set out of the strict update loop order, however i have no idea why this would affect mp3s and not oggs

src/RageSoundReader_MP3.cpp

@@ -594,7 +594,7 @@ int RageSoundReader_MP3::resync()
 RageSoundReader_MP3::RageSoundReader_MP3()
 {
 	mad = new madlib_t;
-	m_bAccurateSync = false;
+	m_bAccurateSync = true;
 
 	mad_stream_init(&mad->Stream);
 	mad_frame_init(&mad->Frame);