Bug#553500: blank window workaround patch works only by accident

[Monty Montgomery]

> Yes, I know my patch was not ideal. Thanks for fixing this bug properly, I'll
> prepare a new package for Debian soon.

Thank you!  I didn't mean to sound harsh, just to the point :-)
(If anything I was annoyed at how the GDK documentation was silently
retconned after the background behavior in GDK changed.)

Cheers,
Monty