<agl/agl.h> => <AGL/agl.h>

With Mac OS X (10.4.10 here) and a case-sensitive filesystem, the

in juce_mac_Windowing.cpp raises a “File not found” compilation error. Replacing it by

fixes the problem.

Since the official name of the framework is full uppercase, I guess this should be changed.

Oops! Thanks for spotting that!