class.c:400
VALUE
rb_mod_included_modules(mod)
    VALUE mod;
{
    VALUE ary = rb_ary_new();
    VALUE p;

    for (p = RCLASS(mod)->super; p; p = RCLASS(p)->super) {
	if (BUILTIN_TYPE(p) == T_ICLASS) {
	    rb_ary_push(ary, RBASIC(p)->klass);
	}
    }
    return ary;
}
