Reduce warnings on OSX

So, as you've probably noticed, building on OSX right now gets you ~150 warnings. The vast majority of these are about QTKit. While getting nagged about QTKit is probably to our benefit, this is making it difficult to actually catch warnings that matter.

This PR suppresses the QTKit warnings, and also replaces a couple of deprecated old-school lines in ofAppGlutWindow that were some 10.7-specifc hack (as far as I can tell?). I've replaced that code with the more modern Obj-C equivalent.

> "...but adam, suppressing warnings is Bad™. You're basically the devil incarnate"

Sure, I've add a `#warning` directive that fires if you're building on 10.9, which IMO gets the point across just fine without filling Xcode's warnings section with what's effectively spam.

There's a few spam-ish warnings left in there about a `gluBuild2DMipmaps` -> `glGenerateMipmap` transition, but... one step at a time :)

Paging @openframeworks/macos