Be smarter about capturing the environment for memoized code

Be smarter about capturing the environment for memoized code

* libguile/memoize.h (SCM_M_CAPTURE_MODULE)
* libguile/memoize.c (MAKMEMO_CAPTURE_MODULE, capture_env):
  (maybe_makmemo_capture_module, memoize): Determine when to capture the
  module on the environment chain at compile-time, instead of at
  runtime.  Introduces a new memoized expression type, capture-module.
  (scm_memoized_expression): Start memoizing with #f as the
  environment.
  (unmemoize): Add unmemoizer.
  (scm_memoize_variable_access_x): Cope with #f as module, and treat as
  the root module (captured before modules were booted).

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