as well as the hash function (formerly the comparison function was hardwired
as memcmp()).  This makes it possible to eliminate the special-purpose
hashtable management code in execGrouping.c in favor of using dynahash to
manage tuple hashtables; which is a win because dynahash knows how to expand
a hashtable when the original size estimate was too small, whereas the
special-purpose code was too stupid to do that.  (See recent gripe from
Stephan Szabo about poor performance when hash table size estimate is way
off.)  Free side benefit: when using string_hash, the default comparison
function is now strncmp() instead of memcmp().  This should eliminate some
part of the overhead associated with larger NAMEDATALEN values.