High-DPI screenshot

[Eric Wasylishen]

Hey,
Here's a screenshot of a patch I'm working on which scales the UI for high DPI 
monitors - I think it's pretty cool :-)

It was surprisingly easy to implement. The actual scaling is done simply by 
changing the bounds and frame rects in GSWindowDecorationView (no changes in 
-back, and it works with cairo/art/xlib). You can set an arbitrary scale factor 
via a GSScaleFactor user default. Other than that, there were just a couple of 
bugs to fix to get it to work (and still some bugs remaining, but it's at least 
usable.)

I'll commit this after the upcoming release.

Cheers,
Eric