Note to self, green handle copy of a Whisker window is somehow borken by
this. I gave myself a walkback (Nil should not have dependents) while
trying to dup a spare of a slightly used Whisker window. 

The magic to making this bug is -
0. File in Whisker, (I have its 4843 update), and both my lines of [FIX].
1. Open up a Whisker browser.
2. Look at a class. 
3. Click on a method|comment to view it. Click it away, and click thrice
for luck (sometimes less, sometimes more?)
4. Green handle copy it. If all goes h^Hwell, it barfed.
5. Smalltalk primitiveGarbageCollect. Object flushDependents "in that
order!"
6. Try green-handling the Whisker again. it should work now. 

Did I just trip on a lurking bug in WeakKeyDictionary?