[gnome-db] input values in SQL view

[Rodrigo Moya <rodrigo gnome-db org>]

Hi

I've just implemented support for input values in the SQL window, so now
you can do things like:

update table set field1 = :field1, field2 = ':field2'

and mergeant will ask you for :field1 and :field2 values.

It works for me so far, but haven't really done a lot of testing, so
please tell me any problems you might find.

cheers