Take care of some differences between the MOP implementations of Lispworks
and SBCL.  Lispworks doesn call (SETF SLOT-VALUE-USING-CLASS) in
SHARED-INITIALIZE, but SBCL does.  Lispworks calls FINALIZE-INHERITANCE
after a class is redefined and a new instance is created, but SBCL doesn't.
All tests now work for Lispworks (5.0) and SBCL (0.9.16).

Some work on a copying GC.