evaluator support for case-lambda

evaluator support for case-lambda

* libguile/memoize.c (patch_case_lambda, scm_m_case_lambda)
  (scm_m_case_lambda_star): Add memoizers for case-lambda and
  case-lambda*.
  (unmemoize): Unmemoize lambdas with multiple arities.

* libguile/eval.c (prepare_boot_closure_env_for_apply):
  (prepare_boot_closure_env_for_eval): Adapt to return both body and
  env, so that case-lambda clauses can be selected appropriately.
  (eval, boot_closure_apply): Adapt callers.

* module/ice-9/eval.scm (make-general-closure): Support multiple
  arities.