Re: Make foo=null a warning by default.

Hello David,

> I assure you that you expression yourself in English a good deal
> better than I do in Portuguese.

Alas, despite a Portuguese "rabbit" name, I cannot speak the language 
which got lost between generations.

About this v3: Patch applies, compiles, "make check" ok.

A few minor comments:

Variable "need_transform_null_equals" may be better named 
"is_null_equals", because there is no "need" of the transformation as 
such, and the expression just checks for the pattern, really.

I'm fine with the off/warn/error/on order.

Doc could mention that the transformation allows compatibility with other 
products, without naming them? Or not.

In doc, the list of valid values on a long line, where the practice seems 
to wrap around after about 80 columns in the XML file.

I notice that the feature was not tested at all before this patch:-(

Maybe there could be one test which results to true, which is the whole 
point of the transformation? eg "SELECT NULL = NULL".

-- 
Fabien.