* Separate GLFbo and GLExt implementations. GLFbo can now be implemented either via vanilla OpenGL3 calls or GL_EXT_framebuffer_*** extensions (OpenGL2.1- only).
* Use modern way of getting supported extensions in core profile.
* Luminance and Alpha formats are not available when running in core profile.
* Bind a dummy vertex array object (VAO) when running in core profile.
* Point sprite mode is always enabled. Since both OpenGL ES 2.0 and OpenGL 3.2 core require it, jME3 is no longer capable of rendering regular points.
* this is required for pregenerated mipmaps in e.g. DDS files
* others checks are added to make sure a zero-length buffer cannot be uploaded (that's an error for now)
