Tested and inspected in 3.9a #6550.  W/o fix, manual test provided locks
up the image as described; w/ fix image is not locked.  Changes one
method and adds another.  Existing DelayTest still passes. Recommend
including.
Any bug/fix that freezes the image deserves a sunit test.  However, I
was unable to convert David's manual test to a well behaved test.  Any
pointers welcome. Here's as far as I got:
DelayTest>>testDelayFailure
	 | bigDelay |
	  self should:
		 	[  bigDelay := Delay forMilliseconds: SmallInteger maxVal + 1.
	  		   [bigDelay wait] fork.
	  		   (Delay forSeconds: 1) wait.
			   Smalltalk garbageCollect
			]
		   raise: Error.