pgsql: Add a check for trigger function with declared arguments.

Log Message:
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Add a check for trigger function with declared arguments. This path
could not be reached before, but now that there is a plpgsql validator
function, it can be. Check is needed to prevent core dump reported by
Satoshi Nagayasu. Besides, this gives a more specific and useful
error message for a fairly common novice error.

Modified Files:
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pgsql/src/pl/plpgsql/src:
pl_comp.c (r1.91 -> r1.92)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_comp.c.diff?r1=1.91&r2=1.92)