psyntax, primitive expander, and memoizer support for letrec*

psyntax, primitive expander, and memoizer support for letrec*

* libguile/expand.c (expand_letrec_helper): Factor out common code.
  (expand_letrec): Use expand_letrec_helper.
  (expand_letrec_star): New primitive syntax: letrec*.

* libguile/memoize.c (memoize): Add memoizer support for in-order letrec
  (letrec*).

* module/ice-9/psyntax.scm (build-letrec): Another arg, `in-order?'.
  (chi-body): Adapt to build-letrec change. We don't yet use letrec* for
  internal definitions.
  (letrec): Adapt to build-letrec change.
  (letrec*): New expander.

* module/ice-9/psyntax-pp.scm: Regenerated.