Added support for creating OpenGL ES 2 and 3 contexts, and updated the OpenGL context creation code to be more robust in general.

If the LOVE_GRAPHICS_USE_OPENGLES environment variable is set, then love will try to create an OpenGL ES context before falling back to regular OpenGL. If it's not set (or set to 0), then the opposite happens except when love is run on backends that should always use OpenGL ES.

--HG--
branch : minor

src/modules/graphics/opengl/Graphics.h

@@ -487,8 +487,6 @@ private:
 
 	static const size_t MAX_USER_STACK_DEPTH = 64;
 
-	bool displayedMinReqWarning;
-
 }; // Graphics
 
 } // opengl