[wxGTK] wxTLW not scrollable (was: segfault with Dialog)

[Robert Roebling]

> Of course, there should still be no crash so we should probably add the
> necessary checks to prevent it from happening -- unless there is a way of
> making wxTLWs scrollable in wxGTK too? Is there, Robert?

We currently implement the scrolling logic in wxWindowGTK::Create
which is not used from within wxTLW::Create. It requires adding
a GtkScrolllWindow underneath the client area (as it is done
for wxWindowGTK) and there is no reason to say that this is not
possible for wxTLW, but since we never officially supported 
built-in scrolling for dialogs during the last before, I see
little reason to start doing so now. I'd like to mention that
we'd support a very non-native "feel" as dialogs only usually
scroll on embedded platforms due to apparent size constraints.

  Robert