nuking GtkData

[Havoc Pennington <hp redhat com>]

Hi,

Propose that we remove GtkData from the inheritance hierarchy; it has
no methods, it has one signal "disconnect" that GtkText connects to,
but AFAICS this signal is never emitted (and whatever purpose it used
to have is surely filled by "destroy" now). Let's make Tooltips and
Adjustment just derive from GtkObject.

Havoc