Moved weak pair code into `weaks.[ch]'.

Moved weak pair code into `weaks.[ch]'.

* libguile/hashtab.c: Don't include <gc/gc_typed.h> and <gc/gc.h>.
  Updated users of weak
  (wcar_cell_descr): Removed.
  (wcdr_cell_descr): Removed.
  (scm_weak_car_cell): Removed.
  (scm_weak_cdr_cell): Removed.
  (scm_doubly_weak_cell): Removed.
  (SCM_WEAK_CELL_*_DELETED_P): Removed.
  (SCM_WEAK_CELL_WORD): Removed.
  (SCM_WEAK_CELL_C[AD]R): Removed.
  (scm_hashtab_prehistory): Don't initialize weak pairs.

* libguile/init.c (scm_i_init_guile): Invoke `scm_weaks_prehistory ()'
  before `scm_hashtab_prehistory ()' in order to initialize weak pairs.

* libguile/weaks.c: Include <gc/gc.h> and <gc/gc_typed.h>.
  (wc[ad]r_cell_descr): New.
  (scm_weak_c[ad]r_pair): New.
  (scm_doubly_weak_pair): New.
  (scm_weaks_prehistory): New.

* libguile/weaks.h (scm_weak_c[ad]r_pair): New declaration.
  (scm_doubly_weak_pair): New declaration.
  (SCM_WEAK_PAIR_WORD_DELETED_P): New.
  (SCM_WEAK_PAIR_CAR_DELETED_P): New.
  (SCM_WEAK_PAIR_CDR_DELETED_P): New.
  (SCM_WEAK_PAIR_DELETED_P): New.
  (SCM_WEAK_PAIR_WORD): New.
  (SCM_WEAK_PAIR_CAR): New.
  (SCM_WEAK_PAIR_CDR): New.

git-archimport-id: lcourtes@laas.fr--2005-libre/guile-core--boehm-gc--1.9--patch-39