Обсуждение: pgsql: Add additional example for interval multiplication.

Log Message:
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Add additional example for interval multiplication.

Fix example for day and hours interval subtraction for new computation
method.

Update interval examples to display zero seconds, which is our default.

Backpatch to 8.1.X.

Modified Files:
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    pgsql/doc/src/sgml:
        func.sgml (r1.298 -> r1.299)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.298&r2=1.299)