[glean-dev] new case for FBO

[He, S. <shu...@in...>]

Hi,
        I've written a glean case for GL_EXT_framebuffer_object. The 
test case is attached.

The test case is categorized into following parts:

                  Functionality:

                     Sanity check (checks max number of supported color 
attachment points, default framebuffer binding, max Renderbuffer Size)

                     Render to texture through single Framebuffer object 
(1D, 2D, 3D, Cube texture, combined with depth/stencil buffer).

                     Render to multiple textures through multiple/single 
Framebuffer object (test render to 2D texture in different usage models).

                     Render to depth texture without color buffer.

                     Render to texture with manual mipmap generation.

            Performance:

                     Compare performance of new style texture through 
FBO with previous glCopyTexImgage style texture

Thanks
    --Shuang