Garbage Collection Riddle

[Eric Dean Tribble <tribble>]

I assume this is the garbage collector version of the problem I
pointed to for purging schemes:  If you call zorch on the original
Bar, the first zap messages clears the strong pointer to the Bar.  The
second zap could cause a garbage collection, and the Bar currently
executing zorch() would be collected even though it is currently in
the midst of executing because it has no strong pointers to it.

Presumably you started all this with the message zip.  In fact this
does seem like a rather bizarre and inlikely construct.  It will only
occur when we have circular structures keeping everything together.  A
particular example that occurs to me is the replaceOLoaf: operation to
replace the child pointer to a loaf in the ent.  This will
conveniently go away when I switch to using become.  Presumably the
same thing happens in the other direction.

dean