* libguile/programs.c (try_parse_arity): New helper, to parse bytecode
  to determine the minimum arity of a function in a cheaper way than
  grovelling through the debug info.  Should speed up all thunk? checks
  and similar.
  (scm_i_program_arity): Simplify.
* libguile/gsubr.h:
* libguile/gsubr.c (scm_i_primitive_arity):
* libguile/foreign.h:
* libguile/foreign.c (scm_i_foreign_arity):