generic tweaks; realizing what the setter slot actually is

generic tweaks; realizing what the setter slot actually is

* libguile/goops.h (scm_si_dispatch_procedure)
  (scm_si_effective_methods): Rename the new generics slots to
  "effective-methods" and "dispatch-procedure".
  (scm_si_generic_setter): Rename this one from "%setter" to "setter",
  and it's not a cache -- it's a pointer to the setter, which is also a
  generic. I didn't realize that before. It's better this way (like it
  always was.)
  (SCM_SET_GENERIC_DISPATCH_PROCEDURE)
  (SCM_CLEAR_GENERIC_EFFECTIVE_METHODS): New helper macros.

* libguile/goops.c (clear_method_cache): Clear the new dispatch
  procedure and the effective methods as well.
  (create_standard_classes): Rename slots, and fix the setter slots.