a different tack for syncase macro representation

a different tack for syncase macro representation

* libguile/macros.c (macro_print): Show syntax-case bindings, if present.
  (macro_mark): Mark the extra two words if they're there.
  (scm_make_syncase_macro, scm_make_extended_syncase_macro): OK! A new
  take at the "how do we represent syncase macros in Guile" problem.
  Whereas we need a disjoint type, but would like it to be compatible
  with old predicates (e.g. `macro?'), and need to be able to extend
  existing syntax definitions (e.g. `cond'), let's add a bit to macros to
  indicate whether they have syncase macro bindings or not, and a fourth
  macro type for native syncase macros.
  (scm_macro_type): Return 'syntax-case for native syntax-case macros.
  Note that other macro types may have syntax-case bindings.
  (scm_macro_name): Return #f if the transformer is not a procedure.
  (scm_syncase_macro_type, scm_syncase_macro_binding): New accessors for
  the syncase macro bindings.

* libguile/macros.h: Add API for syncase macros.

* module/ice-9/boot-9.scm (module-define-keyword!): Adapt to use syncase
  macros, though they are not yet used. Reorder other syncase API.

* module/ice-9/psyntax.scm (chi-expr): Fix syntax-violation invocation.