Simplify variable resolution in the evaluator

Simplify variable resolution in the evaluator

* libguile/expand.c (convert_assignment): Handle creation of the default
  lambda-case body here.

* libguile/eval.c (eval):
* module/ice-9/eval.scm (primitive-eval):

* libguile/memoize.h:
* libguile/memoize.c (MAKMEMO_BOX_REF, MAKMEMO_BOX_SET):
  (MAKMEMO_TOP_BOX, MAKMEMO_MOD_BOX): Refactor all global var resolution
  to go through "resolve".  Add "box-ref" and "box-set!".  Rename
  memoize-variable-access! to %resolve-variable, and don't be
  destructive.