pgsql-server: Example for create function using argument names Gavin

Log Message:
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Example for create function using argument names

Gavin Sherry

Modified Files:
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pgsql-server/doc/src/sgml/ref:
create_function.sgml (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/ref/create_function.sgml.diff?r1=1.57&r2=1.58)