GNOME T-Shirt: Stain Fighting Gtk+

Finished another GNOME t-shirt which should in fact more accurately be described as a Gtk+ t-shirt.

Designing it made me wish Inkscape had diagonal guides. They could be set like orthogonal guides, with a click in and drag from the rulers. To differentiate setting one kind of guide vs. the other, diagonal guide creation could be started with a [Shift] + click or a [Ctrl] + click instead of the regular click alone.