change to format of memoization lambda expressions

change to format of memoization lambda expressions

* libguile/memoize.c (scm_m_lambda, memoize_named_let)
  (scm_memoize_lambda, unmemoize)
* libguile/eval.c (eval, prepare_boot_closure_env_for_apply)
  (prepare_boot_closure_env_for_eval, boot_closure_apply):
* module/ice-9/eval.scm (primitive-eval): Change the format for memoized
  lambda expressions, so as to allow, in the future, case-lambda* to be
  supported by the evaluator.