fix OpenGL detection on Linux, and re-add TTF project to premake

build3/findOpenGLGlewGlut.lua

@@ -1,6 +1,8 @@
 	function findOpenGL()
 		configuration{}
 		if os.is("Linux") then
+			if os.isdir("/usr/include") and os.isfile("/usr/include/GL/gl.h") then return true
+			end
 			return false
 		end
 		--assume OpenGL is available on Mac OSX, Windows etc

build3/premake4.lua

@@ -151,7 +151,7 @@ end
 --		include "../demo/gpu_initialize"
 --		include "../opencl/lds_bank_conflict"
 --		include "../opencl/reduce"
---		include "../btgui/OpenGLTrueTypeFont"
+		include "../btgui/OpenGLTrueTypeFont"
 --		include "../btgui/OpenGLWindow"
 --		include "../demo/ObjLoader"
 --		include "../test/b3DynamicBvhBroadphase"