(struct dirstack_state): Define.

(struct dirstack_state): Define.
To be used in place of these file-scoped globals ...
(dir_stack, len_stack, Active_dir): Remove globals.
(ds_init, ds_free): New functions.
(full_filename): Define.
(full_filename_): Rename from full_filename.

Begin to make AD_* functions more generic.

(AD_push_initial): Don't set status to RM_OK here.
(AD_push): Likewise.
(AD_INIT_OTHER_MEMBERS): Define.
(remove_dir): Define the `status' member manually after each
call to AD_push or AD_push_initial.