Always create the tab container (95% of the code paths would convert the container to a tab container after the fact,
so let's just do it before hand and simplify the code in many places). But create its popupmenu on demand.
Port all inherits() calls to qobject_cast.
Next step is to add unit tests, meanwhile shout if anything broke :)

svn path=/trunk/KDE/kdebase/apps/; revision=673169