pgsql: Back-patch fixes for problems with VACUUM destroying t_ctid

Log Message:
-----------
Back-patch fixes for problems with VACUUM destroying t_ctid chains too soon,
and with insufficient paranoia in code that follows t_ctid links.
This patch covers the 7.3 branch.

Tags:
----
REL7_3_STABLE

Modified Files:
--------------
pgsql/src/backend/access/heap:
heapam.c (r1.149.2.1 -> r1.149.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c.diff?r1=1.149.2.1&r2=1.149.2.2)
pgsql/src/backend/commands:
trigger.c (r1.136.2.2 -> r1.136.2.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c.diff?r1=1.136.2.2&r2=1.136.2.3)
vacuum.c (r1.244 -> r1.244.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c.diff?r1=1.244&r2=1.244.2.1)
pgsql/src/backend/executor:
execMain.c (r1.180.2.2 -> r1.180.2.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execMain.c.diff?r1=1.180.2.2&r2=1.180.2.3)
pgsql/src/backend/utils/time:
tqual.c (r1.61.2.1 -> r1.61.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/time/tqual.c.diff?r1=1.61.2.1&r2=1.61.2.2)
pgsql/src/include/access:
heapam.h (r1.79 -> r1.79.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/heapam.h.diff?r1=1.79&r2=1.79.2.1)
pgsql/src/include/executor:
executor.h (r1.78 -> r1.78.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/executor.h.diff?r1=1.78&r2=1.78.2.1)