Latest invoice window edits gtk+ requirements

[Christian Stimming]

Zitat von Geert Janssens <janssens-geert at telenet.be>:
> Hmm, good point. So far there are no changes yet that require 2.24  
> as far as I
> know. But we'll see what turns up when the DISABLE_DEPRECATED defines are
> used.
>
> Shouldn't we change configure.ac already to require 2.18 ? There is a comment
> in there that this is currently still 2.16 because the windows build didn't
> build with a more recent version. But the windows build is currently using
> 2.24 already.

Yes, I think we can increase our required gtk here. (I'm working with  
2.24 as well during my development.)

Regards,

Christian