Changing audio effects logic so that 'woohoo.au' would not be played
simultaneously with 'excellent.au'. 'excellent.au' takes precedence. If the
end of level is reached when final layers are cleared, which cause
'excellent.au' sound effect, then 'woohoo.au' isn't played. Unfortunately this
repeated logic occurs in four different places. It would be nice to somehow
factor that code into one spot, eventually.