INSERT and parentheses

Hi,

This came up on IRC today and I recall several instances of this during
the last two months or so, so I decided to send a patch. The problem in
question occurs when you have extra parentheses in an INSERT list:

INSERT INTO foo(a,b,c) SELECT (a,b,c) FROM ..; or
INSERT INTO foo(a,b,c) VALUES((0,1,2));

Both of these give you the same error:
ERROR: INSERT has more target columns than expressions

The first version is a lot more common and as it turns out, is sometimes
very hard to spot. This patch attaches a HINT message to these two
cases. The message itself could probably be a lot better, but I can't
think of anything.

Thoughts?

Regards,
Marko Tiikkaja