This function has to be called to enable the full capacity for type
conversions in GtkAda. If this function is not called, then
converting a C widget to an Ada type will not be as exact (for
instance, most C widgets will get converted to a Gtk.Object, instead
of the matching Ada widget. One major exception is Gtk_Label which
will always be recognized by GtkAda).
On the other hand, if you call this function (or with this package),
then your application will 'with' all the GtkAda packages, involving
bigger statically linked executables and a longer elaboration.