By defining the new helper inside _Hashtable_base it doesn't need all
the template parameters to be provided, and by making it only
responsible for checking a possibly-cached hash code it only has to do
one thing. The caller can use the equality predicate itself instead of
duplicating that in the helper template.
* include/bits/hashtable_policy.h (_Equal_helper): Remove.
(_Hashtable_base::_Equal_hash_code): Define new class template.
(_Hashtable_base::_M_equals): Use _Equal_hash_code instead of
_Equal_helper.
From-SVN: r271291
