pgsql: Add support for cross-type hashing in hash index searches and

Log Message:
-----------
Add support for cross-type hashing in hash index searches and hash joins.
Hashing for aggregation purposes still needs work, so it's not time to
mark any cross-type operators as hashable for general use, but these cases
work if the operators are so marked by hand in the system catalogs.

Modified Files:
--------------
pgsql/src/backend/access/hash:
hashsearch.c (r1.47 -> r1.48)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/hash/hashsearch.c.diff?r1=1.47&r2=1.48)
hashutil.c (r1.50 -> r1.51)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/hash/hashutil.c.diff?r1=1.50&r2=1.51)
pgsql/src/backend/executor:
execGrouping.c (r1.23 -> r1.24)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execGrouping.c.diff?r1=1.23&r2=1.24)
nodeHash.c (r1.109 -> r1.110)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeHash.c.diff?r1=1.109&r2=1.110)
nodeHashjoin.c (r1.87 -> r1.88)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeHashjoin.c.diff?r1=1.87&r2=1.88)
nodeSubplan.c (r1.82 -> r1.83)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeSubplan.c.diff?r1=1.82&r2=1.83)
pgsql/src/backend/optimizer/plan:
createplan.c (r1.223 -> r1.224)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c.diff?r1=1.223&r2=1.224)
pgsql/src/backend/utils/cache:
lsyscache.c (r1.146 -> r1.147)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/lsyscache.c.diff?r1=1.146&r2=1.147)
pgsql/src/include/access:
hash.h (r1.75 -> r1.76)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/hash.h.diff?r1=1.75&r2=1.76)
pgsql/src/include/executor:
hashjoin.h (r1.43 -> r1.44)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/hashjoin.h.diff?r1=1.43&r2=1.44)
nodeHash.h (r1.43 -> r1.44)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/nodeHash.h.diff?r1=1.43&r2=1.44)
pgsql/src/include/utils:
lsyscache.h (r1.115 -> r1.116)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/lsyscache.h.diff?r1=1.115&r2=1.116)