Add support for the lineDash API.

Described here:
http://www.w3.org/TR/2dcontext/#dom-context-2d-setlinedash

The test images match on Chrome, but not on Firefox. It looks like
Firefox resets the lineDash to [] when given invalid parameters. My
reading of the spec agrees with Chrome.

-David
You were right, my gcc include-dir is actually pointing to a different folder which seems to be ```/usr/include/c++/4.2.1``` and not ```/usr/include/```.
In the "4.2.1" isnan is not define. The math.h in /usr/include does so.

But i have no idea why this path is set to 4.2.1, ;Maybe a homebrew install ... but i have no clue which one could have done it.