DEPTH_STENCIL internal format is not supported for renderbufferStorage() in ES2 environments

DEPTH_STENCIL internal format is not supported for renderbufferStorage() in ES2 environments.

To repro, run e.g. cellphone example in android, and you will get an OpenGL error about unsupported enum, and the environment map on the cellphone case will not work.

FramebufferRenderbuffer() needs to support DEPTH_STENCIL_ATTACHMENT also.