We need to be able to identify frames that are primitive applications
without assuming that slot 0 in a frame is an SCM value and without
assuming that value is the procedure being applied.

* libguile/gsubr.c (scm_i_primitive_code_p): New helper.
  (scm_i_primitive_arity): Use the new helper.
* libguile/gsubr.h: Declare the new helper.

* libguile/programs.h:
* libguile/programs.c (scm_program_code_p): New function, replacing
  scm_primitive_p.
  (scm_primitive_call_ip): Fix FUNC_NAME definition.

* module/statprof.scm (sample-stack-procs, count-call): Identify
  primitive frames from the IP, not the frame-procedure.  Avoids the
  assumption that slot 0 in a frame is a SCM value.
  (statprof-proc-call-data): Adapt to primitive-code? change.

* module/system/vm/frame.scm (frame-call-representation): Identify
  primitive frames from the IP, not the closure.  Still more work to do
  here to avoid assuming slot 0 is a procedure.

* module/system/vm/program.scm: Export primitive-code? instead of
  primitive?.
  (program-arguments-alist, program-arguments-alists): Identify
  primitives from the code instead of the flags on the program.  Not
  sure this is a great change, but it does avoid having to define a
  primitive? predicate in Scheme.