* hooks.c (scm_c_hook_add): Fixed bug in append mode.

* hooks.c (scm_c_hook_add): Fixed bug in append mode.

* environments.c (obarray_enter, obarray_retrieve, obarray_remove,
leaf_environment_fold, obarray_remove_all): Use hashtable
accessors.

* gc.c (scm_init_storage): Moved hook initialization to
scm_storage_prehistory.
(scm_storage_prehistory): New function.
(scm_igc): Added commentary about placement of
scm_after_sweep_c_hook.

* gc-mark.c (scm_mark_all): Use hashtable accessors.
(scm_gc_mark_dependencies): Use SCM_WVECT_WEAK_KEY_P and
SCM_WVECT_WEAK_VALUE_P.

* hashtab.c, hashtab.h (scm_hash_for_each, scm_hash_map): New
functions.
(scm_vector_to_hash_table, scm_c_make_resizing_hash_table):
Removed.
(scm_make_weak_key_hash_table, scm_make_weak_value_hash_table,
scm_make_doubly_weak_hash_table): Moved here from weaks.c.

* init.c (scm_init_guile_1): Removed call to scm_init_weaks; Added
calls to scm_storage_prehistory and scm_hashtab_prehistory.

* modules.c (module-reverse-lookup): Use hashtable accessors.

* symbols.c, symbols.h (scm_i_hash_symbol): New function.

* weaks.c, weaks.h (scm_make_weak_key_alist_vector,
scm_make_weak_value_alist_vector,
scm_make_doubly_weak_alist_vector): New functions.

* weaks.c (scm_init_weaks_builtins): New function.

* weaks.h (SCM_WVECTF_WEAK_KEY, SCM_WVECTF_WEAK_VALUE,
SCM_WVECTF_NOSCAN, SCM_WVECT_WEAK_KEY_P, SCM_WVECT_WEAK_VALUE_P,
SCM_WVECT_NOSCAN_P): New macros.

* weaks.c (scm_scan_weak_vectors):  Use SCM_WVECT_WEAK_KEY_P
and SCM_WVECT_WEAK_VALUE_P.

* weaks.c, weaks.h (scm_i_allocate_weak_vector): Renamed from
allocate_weak_vector and exported.

* Makefile.am (ice9_sources): Added weak-vector.scm.

* weak-vector.scm: New file.

* boot-9.scm (module-clear!): Use hash-clear!.
(module-for-each): Use hash-for-each.
(module-map): Use hash-map.