[gtkada] Gtkada 2.0 bug report

[Arnaud Charlet]

> It seems that the functions
> Gtk.Pixmap.Get_Mask and Gtk.Pixmap.Get_Pixmap were forgotten,
> breaking compatibility with 1.2.

Right, see file docs/2.0-transition.txt

1.2 and 2.0 are *not* compatible (this was a Gtk+ design decision, followed
by GtkAda).

On the other hand, Gtk+ 2.0 and 2.2 are compatible.

Many things are similar, but there have been substantial API changes.
In this case, it is simply a matter of changing the name of the function,
so the change is easy.

Arno