pgsql: Fix to_date()/to_timestamp() 'D' field for day of week, was off

Log Message:
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Fix to_date()/to_timestamp() 'D' field for day of week, was off by one.
Converting from char using 'D' doesn't make lots of sense, of course.

Report from Brendan Jurd.

Modified Files:
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pgsql/src/backend/utils/adt:
formatting.c (r1.123 -> r1.124)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/formatting.c.diff?r1=1.123&r2=1.124)