client side syntax error localisation for psql (v1)

Dear patchers,

Please find attached my first attempt at providing a localisation
information on the client side for syntax errors in "psql". Basically, one
function is added which takes care of the burden. I put a lot of
comments in the function to try make it clear what is going on.

It validates for me against current cvs head.

I've also added new regression tests in "errors.sql".

Although I have taken great and painful care to deal with multi-byte
encodings, I'm not sure how I can validate that, as I don't have some
japanese terminal to play with.

Have a nice day,

--
Fabien Coelho - coelho(at)cri(dot)ensmp(dot)fr