pgsql: Back-patch the 8.3 fix that prohibits TRUNCATE, CLUSTER, and

Log Message:
-----------
Back-patch the 8.3 fix that prohibits TRUNCATE, CLUSTER, and REINDEX when the
current transaction has any open references to the target relation or index
(implying it has an active query using the relation).  Also back-patch the
8.2 fix that prohibits TRUNCATE and CLUSTER when there are pending
AFTER-trigger events.  Per suggestion from Heikki.

Tags:
----
REL8_0_STABLE

Modified Files:
--------------
    pgsql/src/backend/catalog:
        index.c (r1.244.4.3 -> r1.244.4.4)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/index.c?r1=1.244.4.3&r2=1.244.4.4)
    pgsql/src/backend/commands:
        cluster.c (r1.131.4.2 -> r1.131.4.3)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/cluster.c?r1=1.131.4.2&r2=1.131.4.3)
        tablecmds.c (r1.142.4.9 -> r1.142.4.10)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/tablecmds.c?r1=1.142.4.9&r2=1.142.4.10)
        trigger.c (r1.177.4.4 -> r1.177.4.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c?r1=1.177.4.4&r2=1.177.4.5)
    pgsql/src/include/commands:
        tablecmds.h (r1.21 -> r1.21.4.1)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/tablecmds.h?r1=1.21&r2=1.21.4.1)
        trigger.h (r1.51.4.1 -> r1.51.4.2)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/trigger.h?r1=1.51.4.1&r2=1.51.4.2)