pgsql: Improve plpgsql's error message when a datatype declaration is

Log Message:
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Improve plpgsql's error message when a datatype declaration is omitted.
Per example from Jeff Ross.

Modified Files:
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pgsql/src/pl/plpgsql/src:
gram.y (r1.98 -> r1.99)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/gram.y.diff?r1=1.98&r2=1.99)