ofxAppEGLWindow fix 

ofxAppEGLWindow fix for seamless compatibility with recent RPI firmware updates.

This will replace the `sed` based text replace workaround inhttp://www.openframeworks.cc/setup/raspberrypi/Raspberry-Pi-Getting-Started.html

@jvcleave @danthemellowman -- can you test this with your current setup (both old and post https://github.com/Hexxeh/rpi-firmware/commit/ca3703d2d282ac96a97650e2e496276727e1b65b firmwares)?