[gnome-db] Patch for NOT NULL attribute

["Vivien" <malerba gnome-db org>]

Hi!

You posted a patch for the Postgres provider which returns FALSE when a
table's column can't be NULL. It used to return TRUE (to the question
"Does the field have a NOT NULL constraint?").

The libgda doc is not very clear on this point, but I think it's worth
deciding how to interpret the "not null?" field and make sure all the
providers implement the same.

If the common understanding is that a TRUE value means that the
corresponding field can have a NULL value, then so be it. What do you
think?

Cheers,

Vivien