pgsql: Fix handling of CC (century) format spec in to_date/to_char.

Log Message:
-----------
Fix handling of CC (century) format spec in to_date/to_char. According to
standard convention the 21st century runs from 2001-2100, not 2000-2099,
so make it work like that. Per bug #2885 from Akio Iwaasa.

Backpatch to 8.2, but no further, since this is really a definitional
change; users of older branches are probably more interested in stability.

Modified Files:
--------------
pgsql/doc/src/sgml:
func.sgml (r1.349 -> r1.350)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.349&r2=1.350)
pgsql/src/backend/utils/adt:
formatting.c (r1.117 -> r1.118)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/formatting.c.diff?r1=1.117&r2=1.118)
pgsql/src/test/regress/expected:
timestamp.out (r1.31 -> r1.32)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamp.out.diff?r1=1.31&r2=1.32)
timestamptz.out (r1.21 -> r1.22)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamptz.out.diff?r1=1.21&r2=1.22)