de-nargs struct scm_objcode; procedure-property refactor

de-nargs struct scm_objcode; procedure-property refactor

* libguile/objcodes.h (struct scm_objcode): Remove nargs, nrest, and
  nlocs, as they are no longer needed. Also obviates the need for a
  padding word.

* libguile/procs.c (scm_thunk_p): Use scm_i_program_arity for programs.

* libguile/procprop.c (scm_i_procedure_arity): Use scm_i_program_arity
  for programs.
  (scm_procedure_properties, scm_set_procedure_properties_x)
  (scm_procedure_property, scm_set_procedure_property_x): Rework so that
  non-closure properties are stored directly in a weak hash, instead of
  needing a weak hash of "stand-in" closures to hold the properties. Fix
  docstrings also.

* libguile/root.h (scm_stand_in_procs): Remove from the scm_sys_protects
  set. Actually with libGC, we should be able to store the elements of
  scm_sys_protects directly as global variables.
* libguile/gc.c (scm_init_storage): Remove scm_stand_in_procs
  initialization.

* libguile/programs.c (scm_i_program_arity): New private accessor, tries
  to determine the "minimum arity" of a program.

* libguile/vm.c (really_make_boot_program): Adapt to changes in
  struct scm_objcode.

* module/language/assembly.scm (*program-header-len*, byte-length):
* module/language/assembly/compile-bytecode.scm (write-bytecode):
* module/language/assembly/decompile-bytecode.scm (decode-load-program):
* module/language/assembly/disassemble.scm (disassemble-load-program):
  Adapt to changes in objcode.

* module/system/xref.scm (program-callee-rev-vars): Adapt to changes in
  assembly.

* module/language/glil.scm: Remove nargs, nrest, and nlocs from
  glil-program.

* module/language/glil/compile-assembly.scm (make-meta, glil->assembly):
* module/language/glil/decompile-assembly.scm (decompile-toplevel):
  (decompile-load-program): Adapt to changes in GLIL and assembly.

* module/language/tree-il/compile-glil.scm (flatten-lambda): Adapt to
  changes in GLIL.

* test-suite/tests/asm-to-bytecode.test: Adapt to assembly and bytecode
  changes.
* test-suite/tests/tree-il.test: Adapt to GLIL changes.