pgsql: Implement syntax for transition tables in AFTER triggers.

Implement syntax for transition tables in AFTER triggers.

This is infrastructure for the complete SQL standard feature. No
support is included at this point for execution nodes or PLs. The
intent is to add that soon.

As this patch leaves things, standard syntax can create tuplestores
to contain old and/or new versions of rows affected by a statement.
References to these tuplestores are in the TriggerData structure.
C triggers can access the tuplestores directly, so they are usable,
but they cannot yet be referenced within a SQL statement.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8c48375e5f43ebd832f93c9166d1fe0e639ff806

Modified Files
--------------
doc/src/sgml/catalogs.sgml | 16 ++
doc/src/sgml/ref/create_trigger.sgml | 94 ++++++++--
src/backend/commands/tablecmds.c | 5 +-
src/backend/commands/trigger.c | 327 +++++++++++++++++++++++++++++++++--
src/backend/nodes/copyfuncs.c | 16 ++
src/backend/nodes/equalfuncs.c | 14 ++
src/backend/nodes/outfuncs.c | 13 ++
src/backend/parser/gram.y | 70 +++++++-
src/backend/utils/adt/ruleutils.c | 23 +++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_trigger.h | 13 +-
src/include/commands/trigger.h | 2 +
src/include/nodes/nodes.h | 1 +
src/include/nodes/parsenodes.h | 17 ++
src/include/parser/kwlist.h | 3 +
src/include/utils/reltrigger.h | 7 +
16 files changed, 580 insertions(+), 43 deletions(-)