Linux and OpenGL ES 2.0

I tried to get Linux 64bit and OpenGL ES 2.0 working and did it in a hackish manner, because I just needed it fast. The steps to get it done:

• compile and include a libglfw3.a with GLFW_USE_EGL = true and GLFW_CLIENT_LIBRARY = glesv2

In ofAppRunner.cpp:

• include ofAppEGLWindow.h, so in cases were defined(TARGET_RASPBERRY_PI) add || defined(TARGET_OPENGLES)
• don't include "glu.h" in ofGraphics.cpp

In ofConstants.h:

• move the #ifdef TARGET_OPENGLES up such that only GLES and EGL is included, not X11

In config.linux.common.mk:

• I forced PLATFORM_DEFINES = TARGET_OPENGLES
• removed PLATFORM_CORE_EXCLUSIONS += $(OF_LIBS_PATH)/openFrameworks/app/ofAppEGLWindow.cpp
• forced PLATFORM_LIBRARIES = EGL Xinerama for correct libglfw3.a linking
• removed PLATFORM_LIBRARIES += glut for #ifneq ($(LINUX_ARM),1)

One has to make the makefiles and the ifdefs cleaner in differenciating between TARGET_LINUX, TARGET_ARM, TARGET_OPENGLES and such. There are many implicit assumptions tangled up in them.