Define functions that are missing for CGContextCanvas [+1]

I found a few functions that are defined, as documented, but only when the canvas feature is not available:

* [CGContextAddLines](http://cappuccino.org/learn/documentation/group__coregraphics.html#ga0ca6b203cebf8ac7752c49e8c3300876)
* [CGContextStrokeRectWithWidth](http://cappuccino.org/learn/documentation/group__coregraphics.html#ga77346891155c2ce6db56dfba94d4a0d4)
* [CGContextAddQuadCurveToPoint](http://cappuccino.org/learn/documentation/group__coregraphics.html#ga4a84c8201ae6dbfd7831d48c6455eced)

I've added definitions for these to the canvas-enabled backend.

This [AppController.j](https://gist.github.com/1376833) can be used to test all three functions.