Use double-cells to store subrs.

Use double-cells to store subrs.

* libguile/procs.c (scm_subr_table, scm_subr_table_size,
  scm_subr_table_room, subr_table_gc_hint, scm_init_subr_table): Remove.
  (scm_c_make_subr): Simply return a double-cell, with the procedure
  name and properties stored in a two-element array.

* libguile/init.c (scm_i_init_guile): Remove call to
  `scm_init_subr_table ()'.

* libguile/procs.h (SCM_SUBR_META_INFO): New macro.
  (SCM_SNAME, SCM_SUBR_PROPS): Use it.
  (SCM_SUBR_GENERIC, SCM_SET_SUBR_GENERIC, SCM_SET_SUBR_GENERIC_LOC):
  Update.
  (scm_t_subr_entry, SCM_SUBR_ENTRY, SCM_SUBRNUM, scm_subr_table,
  scm_init_subr_table): Remove.