Added an untested shader for YV12 textures

Try to create an OpenGL ES 2.0 context on Android and successfully fall back to OpenGL ES 1.1 if that fails.

This is easier for people to set up and work with, and is more conformant to the way desktop OpenGL works.

You don't need to copy the pixels into the streaming texture's pixel data.  This behavior is defined specifically to optimize the UpdateTexture path.

Prefer the OpenGL ES 2.0 context when it's available, make it possible to create an OpenGL 2.0 context on iPhoneOS

--HG--
rename : src/video/SDL_glfuncs.h => src/render/opengl/SDL_glfuncs.h