Tentative fix to errors in new versions of oF related to ofPixels

[andyinabox]

This PR addresses #5. It's hacked together with a machete and duct tape, but the test project seems to building correctly.

[andyinabox]

I should note that I'm on openFrameworks 0.9.8, Xcode 8.2.1. I'm not sure what kind of impact this will have on other environments....