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

Log Message:
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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.

Tags:
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REL8_2_STABLE

Modified Files:
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pgsql/doc/src/sgml:
func.sgml (r1.347 -> r1.347.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.347&r2=1.347.2.1)
pgsql/src/backend/utils/adt:
formatting.c (r1.116 -> r1.116.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/formatting.c.diff?r1=1.116&r2=1.116.2.1)
pgsql/src/test/regress/expected:
timestamp.out (r1.31 -> r1.31.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamp.out.diff?r1=1.31&r2=1.31.2.1)
timestamptz.out (r1.21 -> r1.21.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamptz.out.diff?r1=1.21&r2=1.21.2.1)