pgsql: Add statement_timestamp(), clock_timestamp(), and

Log Message:
-----------
Add statement_timestamp(), clock_timestamp(), and
transaction_timestamp() (just like now()).

Also update statement_timeout() to mention it is statement arrival time
that is measured.

Catalog version updated.

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.55 -> r1.56)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.55&r2=1.56)
func.sgml (r1.314 -> r1.315)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.314&r2=1.315)
pgsql/src/backend/access/transam:
xact.c (r1.219 -> r1.220)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xact.c.diff?r1=1.219&r2=1.220)
pgsql/src/backend/tcop:
postgres.c (r1.485 -> r1.486)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c.diff?r1=1.485&r2=1.486)
pgsql/src/backend/utils/adt:
timestamp.c (r1.162 -> r1.163)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/timestamp.c.diff?r1=1.162&r2=1.163)
pgsql/src/include/access:
xact.h (r1.81 -> r1.82)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/xact.h.diff?r1=1.81&r2=1.82)
pgsql/src/include/catalog:
catversion.h (r1.323 -> r1.324)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.323&r2=1.324)
pg_proc.h (r1.405 -> r1.406)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.405&r2=1.406)
pgsql/src/include/utils:
timestamp.h (r1.59 -> r1.60)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/timestamp.h.diff?r1=1.59&r2=1.60)