There's no top-level dialogue any more, so we need some way to
clean up after ourselves.

Set the default icon for child windows as well, when setting the
panel's icon.

Align buttons "Print Test Page", "Clean Print Heads" and
"Disable Printer" with check button "Default".
Add "Queue" label to print jobs' GtkExpander.

And make sure that the dialogue is destroyed when clicking its
close titlebar button.

Remove some memory leaks.

'Change constrast' should be 'Change contrast'. String change !

It needs some convincing to let itself be attached...

The shell doesn't allow to resize attached dialogs, so we don't
want to show resize grips.

Clean up that mess of a code somewhat.

By making the whole panel bigger. Might work-around a GTK+ bug, we
won't know for now...

But non-NULL. Handle that case.

This has nothing to do here.

Resolves #640068

If the changed signal was emitted again before we got a chance
to create the language dialogue in the idle handler, we'd end up
with two (or more) dialogues.

Otherwise we still have some left-over widgets being parented.