* tree.h (mark_tree_hashtable): New function.
* tree.c (mark_tree_hashtable_entry): New function.
(mark_tree_hashtable): Likewise.
* tree.c (struct list_hash): Remove.
(list_hash_table): Make it be an htab.
(struct list_proxy): New type.
(list_hash_eq): New function.
(list_hash_pieces): Renamed from ...
(list_hash): ... this.
(list_hash_lookup): Remove.
(list_hash_add): Remove.
(hash_tree_cons): Use the generic hashtable.
(mark_list_hash): Remove.
(init_tree): Create the hashtable.
From-SVN: r37783
