[IMP] Improve view validation to based on fields_view_get rendering, not just raw...

[IMP] Improve view validation to based on fields_view_get rendering, not just raw arch

This will allow improved validation of inherited
views, which is not possible when only the raw
arch is validated on its own - without context
many things cannot be verified.
Calling fields_view_get() also catches early all
mistakes that require dynamic validation, like
wrong XPath expressions (parent view contains
no match).
In order to have current addons pass the improved
validation the RNG had to be fixed to support
the new @modifiers attribute added by fields_view_get()
itself on many view elements, and a few missing
valid attributes, like @invisible on <filter>
and <group>. The latter had never been used
as part of the view architecture but appear
as a result of the handling of @groups
restrictions on view elements, and must
be allowed by the RNG schema.

bzr revid: odo@openerp.com-20120614144633-31c642s7q7f28o6b