pgsql: Add timezone offset output option to to_char()

Add timezone offset output option to to_char()
Add ability for to_char() to output the timezone's UTC offset (OF).  We
already have the ability to return the timezone abbeviation (TZ/tz).
Per request from Andrew Dunstan

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/7408c5d29b53fbeae0d88ab8121a42c3b4d9ed64

Modified Files
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doc/src/sgml/func.sgml             |    4 ++++
src/backend/utils/adt/formatting.c |   17 +++++++++++++++--
2 files changed, 19 insertions(+), 2 deletions(-)