pgsql: RESET SESSION, plus related new DDL commands.

Log Message:
-----------
RESET SESSION, plus related new DDL commands. Patch from Marko Kreen,
reviewed by Neil Conway. This patch adds the following DDL command
variants: RESET SESSION, RESET TEMP, RESET PLANS, CLOSE ALL, and
DEALLOCATE ALL. RESET SESSION is intended for use by connection
pool software and the like, in order to reset a client session
to something close to its initial state.

Note that while most of these command variants can be executed
inside a transaction block (but are not transaction-aware!),
RESET SESSION cannot. While this is inconsistent, it is intended
to catch programmer mistakes: RESET SESSION in an open transaction
block is probably unintended.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
close.sgml (r1.24 -> r1.25)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/close.sgml.diff?r1=1.24&r2=1.25)
deallocate.sgml (r1.9 -> r1.10)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/deallocate.sgml.diff?r1=1.9&r2=1.10)
reset.sgml (r1.32 -> r1.33)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/reset.sgml.diff?r1=1.32&r2=1.33)
pgsql/src/backend/catalog:
namespace.c (r1.93 -> r1.94)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/namespace.c.diff?r1=1.93&r2=1.94)
pgsql/src/backend/commands:
async.c (r1.135 -> r1.136)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/async.c.diff?r1=1.135&r2=1.136)
portalcmds.c (r1.62 -> r1.63)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/portalcmds.c.diff?r1=1.62&r2=1.63)
prepare.c (r1.70 -> r1.71)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/prepare.c.diff?r1=1.70&r2=1.71)
pgsql/src/backend/parser:
gram.y (r2.587 -> r2.588)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.587&r2=2.588)
pgsql/src/backend/tcop:
utility.c (r1.276 -> r1.277)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/utility.c.diff?r1=1.276&r2=1.277)
pgsql/src/backend/utils/cache:
plancache.c (r1.5 -> r1.6)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/plancache.c.diff?r1=1.5&r2=1.6)
pgsql/src/backend/utils/misc:
guc.c (r1.383 -> r1.384)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.383&r2=1.384)
pgsql/src/backend/utils/mmgr:
portalmem.c (r1.100 -> r1.101)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mmgr/portalmem.c.diff?r1=1.100&r2=1.101)
pgsql/src/include/catalog:
namespace.h (r1.45 -> r1.46)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/namespace.h.diff?r1=1.45&r2=1.46)
pgsql/src/include/commands:
async.h (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/async.h.diff?r1=1.34&r2=1.35)
prepare.h (r1.25 -> r1.26)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/commands/prepare.h.diff?r1=1.25&r2=1.26)
pgsql/src/include/nodes:
parsenodes.h (r1.344 -> r1.345)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h.diff?r1=1.344&r2=1.345)
pgsql/src/include/utils:
guc.h (r1.80 -> r1.81)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h.diff?r1=1.80&r2=1.81)
plancache.h (r1.4 -> r1.5)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/plancache.h.diff?r1=1.4&r2=1.5)
portal.h (r1.74 -> r1.75)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/portal.h.diff?r1=1.74&r2=1.75)
pgsql/src/test/regress/expected:
guc.out (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/guc.out.diff?r1=1.2&r2=1.3)
portals.out (r1.11 -> r1.12)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/portals.out.diff?r1=1.11&r2=1.12)
prepare.out (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/prepare.out.diff?r1=1.12&r2=1.13)
pgsql/src/test/regress/sql:
guc.sql (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/guc.sql.diff?r1=1.2&r2=1.3)
portals.sql (r1.8 -> r1.9)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/portals.sql.diff?r1=1.8&r2=1.9)
prepare.sql (r1.4 -> r1.5)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/prepare.sql.diff?r1=1.4&r2=1.5)