When the notebook page does not have a label, it should not fallback to
asking its child accessible for extent, since the child might be asking
exactly the converse when it is a socket, thus getting in an infinite
loop. When the page does not have a label, is does not really make sense to
give it an extent anyway.
Fixes atk#18
This commit exposes the get_type() functions and standard
headers for accessible implementations. This makes it possible
to derive from the GTK accessible implementations without
GType magic tricks. This is necessary, because we require the
a11y type hierarchy to be parallel to the widget type hierarchy.
So, if you derive a widget and need to adjust its a11y implementation,
you have to be able to derive its accessible implementation.
This commit probably exposes more than is absolutely necessary,
it also exposes accessibles of widgets that are unlikely candidates
for deriving from.
Explicitly set the notebook page object as the accessible parent
of the page, otherwise, AtkObject follows the widget parents chain
and makes the notebook accessible the parent.