universal_include.h: use case sensitive include for glext.h
universal_include.h: use case sensitive include for glext.h

Signed-off-by: Steven Noonan <4068f0880b399410602d694b3cc711c8a8f4727e@uplinklabs.net>

tycho/cerberus,tycho/cerberus,tycho/cerberus,tycho/cerberus