pgsql: Properly mark mergeable/hashable equality operators (found by

Log Message:
-----------
Properly mark mergeable/hashable equality operators (found by opr_sanity
testing). Combine the formerly independent opclasses for the various
ISN types into opfamilies. The latter causes some extra bleating from
opr_sanity, since the module doesn't provide complete sets of cross-type
operators, but it's still a good idea because it will give the planner
more information to work with. The missing cross-type operators no longer
pose a risk of unexpected planner errors in 8.3, so there's no need to
insist on filling them in (and I gather it wouldn't be very sound
semantically to add them all).

Modified Files:
--------------
pgsql/contrib/isn:
isn.sql.in (r1.5 -> r1.6)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/isn/isn.sql.in?r1=1.5&r2=1.6)