Does nothing particular, except get few informations from the registeredwindow.
ctypes-utils.jsm needs to be ironed out (ABI used for .so version and lib type
for .dll), and we'll probably have problems when declaring callbacks
(ctypes.stdcall_abi on 32bits ?).
Although we can re-construct a gdk.GdkWindow.ptr from natvieHandle (address of
the actual GdkWindow), we can't seem to be able to use it. For ex.,
gdk_window_get_user_data(), which should return a pointer to the corresponding
GtkWindow, returns strange adresses with our re-constructed pointer (0x11,
0x19, 0x0, ...)
...and despite the fact that both the "original" gdk.GdkWindow.ptr and the
re-constructed one do point to the same address, and that GDK_IS_WINDOW (macro
here wrapped into an embedded lib) is returning true for both pointers...
