Fix hash table overallocation etc.

Fix hash table overallocation etc.

* src/fns.c (set_hash_key_and_value, set_hash_next)
(set_hash_hash, set_hash_index): Remove.  All uses removed.
(maybe_resize_hash_table): Don’t update h->next until it’s
known that all the allocations succeeded, to avoid trashing
the hash table if memory is exhausted.  Don’t overallocate the
other vectors.  Don’t output growth message if the hash table
didn’t actually grow due to allocation failure.  Assume C99
decls after statements.