[FIX] It is possible to mention an undeclared column in a domain.

Actually, this seems to be used for the logging columns
which are in database but not necessarily in _columns.
This is ugly and a warning is now issued.

lp bug: https://launchpad.net/bugs/857105 fixed

bzr revid: vmt@openerp.com-20110923101839-ko0s7ekt4dlyvrx2