[FIX] groupby on editable list

[FIX] groupby on editable list

Because of the "meta" columns (e.g. group name column),
ListView#columns would end up with a different number of elements than
ListView#fields_view.arch.children, and when zipping them together (to
build the form view for edition) things wouldn't match anymore.

It would seem simply filtering out meta columns (and only keep those
actually specified by the view) is sufficient to fix the issue and
have everything line up again. I'm midly impressed.

bzr revid: xmo@openerp.com-20121129131301-scc38i4l55ea7lis