pgsql: Improve EXPLAIN ANALYZE to show the time spent in each trigger

Log Message:
-----------
Improve EXPLAIN ANALYZE to show the time spent in each trigger when
executing a statement that fires triggers. Formerly this time was
included in "Total runtime" but not otherwise accounted for.
As a side benefit, we avoid re-opening relations when firing non-deferred
AFTER triggers, because the trigger code can re-use the main executor's
ResultRelInfo data structure.

Modified Files:
--------------
pgsql/doc/src/sgml:
perform.sgml (r1.50 -> r1.51)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/perform.sgml.diff?r1=1.50&r2=1.51)
pgsql/src/backend/catalog:
pg_constraint.c (r1.22 -> r1.23)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/pg_constraint.c.diff?r1=1.22&r2=1.23)
pgsql/src/backend/commands:
copy.c (r1.238 -> r1.239)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/copy.c.diff?r1=1.238&r2=1.239)
explain.c (r1.130 -> r1.131)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/explain.c.diff?r1=1.130&r2=1.131)
portalcmds.c (r1.38 -> r1.39)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/portalcmds.c.diff?r1=1.38&r2=1.39)
trigger.c (r1.180 -> r1.181)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c.diff?r1=1.180&r2=1.181)
pgsql/src/backend/executor:
execMain.c (r1.243 -> r1.244)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execMain.c.diff?r1=1.243&r2=1.244)
execProcnode.c (r1.46 -> r1.47)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execProcnode.c.diff?r1=1.46&r2=1.47)
functions.c (r1.92 -> r1.93)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/functions.c.diff?r1=1.92&r2=1.93)
instrument.c (r1.10 -> r1.11)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/instrument.c.diff?r1=1.10&r2=1.11)
spi.c (r1.135 -> r1.136)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/spi.c.diff?r1=1.135&r2=1.136)
pgsql/src/backend/tcop:
pquery.c (r1.92 -> r1.93)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/pquery.c.diff?r1=1.92&r2=1.93)
pgsql/src/include/catalog:
pg_constraint.h (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_constraint.h.diff?r1=1.14&r2=1.15)
pgsql/src/include/commands:
trigger.h (r1.51 -> r1.52)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/trigger.h.diff?r1=1.51&r2=1.52)
pgsql/src/include/executor:
instrument.h (r1.9 -> r1.10)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/instrument.h.diff?r1=1.9&r2=1.10)
pgsql/src/include/nodes:
execnodes.h (r1.124 -> r1.125)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/execnodes.h.diff?r1=1.124&r2=1.125)