pgsql: Update ANSI INTERVAL section: < * Add support for ANSI time

Log Message:
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Update ANSI INTERVAL section:

< * Add support for ANSI time INTERVAL syntax, INTERVAL '1 2:03:04' DAY TO SECOND
< * Add support for ANSI date INTERVAL syntax, INTERVAL '20-6' YEAR TO MONTH
< * Process mixed ANSI/PG INTERVAL syntax, and round value to requested precision
<
< Interpret INTERVAL '1 year' MONTH as CAST (INTERVAL '1 year' AS INTERVAL
< MONTH), and this should return '12 months'
<
< * Interpret INTERVAL '1:30' MINUTE TO SECOND as '1 minute 30 seconds'
> * Add ANSI INTERVAL handling
> o Add support for day-time syntax, INTERVAL '1 2:03:04'
> DAY TO SECOND
> o Add support for year-month syntax, INTERVAL '50-6' YEAR TO MONTH
> o Process mixed ANSI/PG syntax, and round value to requested
> precision or generate an error
> o Interpret INTERVAL '1 year' MONTH as CAST (INTERVAL '1 year' AS
> INTERVAL MONTH), and this should return '12 months'
> o Interpret INTERVAL '1:30' MINUTE TO SECOND as '1 minute 30 seconds'
> o Support precision, CREATE TABLE foo (a INTERVAL MONTH(3))

Modified Files:
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pgsql/doc:
TODO (r1.1479 -> r1.1480)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1479&r2=1.1480)