one more bug:

in AbstractSound the method

, aSound
	"Return the concatenation of the receiver and the argument sound."

	^ SequentialSound new
		add: self;
		add: aSound


...does not work because the method SequentialSound>>#add: has been 
modified to return the added sound, instead of the receiver:

add: aSound

	sounds := sounds copyWith: aSound.
	^aSound


previously (in 3.8 for example) it was:


add: aSound

	sounds _ sounds copyWith: aSound.


Stef