Construction vtables in layout document

[Jim Dehnert]

I've incorporated changes from Coleen's proposal in the layout document,
in a format that should allow easy comparison.  There are no substantive
wording changes (yet :-), but I did modify the pseudo-code for the
constructor a bit to clarify.  Coleen, can you please verify that it
actually clarifies, and isn't wrong?

Jim

-		Jim Dehnert  x3-4272