definitions of the rudimentary classes described by objects.h.
* objects.c, objects.h (scm_entity_p): New procedure. Together
with the predicates scm_procedure_p and scm_struct_p, this
predicate makes it possible to differ between structs, entities
and operators.
make_class_object; exported; error checking moved to
scm_make_class_object and scm_make_subclass_object.
(scm_make_class_object, scm_make_subclass_object): Use
scm_i_make_class_object.
(scm_make_subclass_object): Let the subclass have same metaclass
as the superclass.
Some indentation fixes.
* objects.h (SCM_METACLASS_STANDARD_LAYOUT): Printer field is no
longer a user field; New field: class_flags.
* objets.c, objects.h: New metaclass: scm_metaclass_operator.