Issue: DYNAMIC-EXTENT (Version 2)

[gz@spt.entity.com (Gail Zacharias)]

     Actually, a blurry issue is whether
      (LENGTH (LIST (LET ((X (LIST 1 2 3))) (DECLARE (DYNAMIC-EXTENT X)) X)))
      => 1
     is well-defined. I refer to these stack-allocated things as being invalid
     return values, but in fact we might want to say that they're ok to return
     but that you just can't do any serious operations on them (ie, you can't
     expect them to still be lists, etc.) Can anyone imagine a pointer into
     unallocated stack causing problems for their GC? If so, we could be more
     clear on this point.

Yes, this would lose badly in our system if the outer call to LIST were to gc.
It's not pointing into unallocated stack that's the problem, it's pointing to
reallocated stack.