handle non-standard slot allocations when updating classes
* Refactor layout comparison to work on the effective slot definition list(s)
directly -- easier to understand.
* When new slots with custom allocation are added, add their names to the
"added" list for UPDATE-INSTANCE-FOR-REDEFINED-CLASS. This is not specified
by ANSI, but unless we do this those slots don't get initialized.
Removing custom slots is hairier, as is changing a custom slot into
a normal slot. Add some tests that poke in this area as well...
* Replace wrapper-instance-slot-layout and wrapper-class-slots with the
CLASS-SLOTS lists -- saves space and makes things easier to understand.
Has a small performance cost for updating instances and SLOT-MISSING. Will
refactor again if this is critical in the real world.