enable OES derivatives extension in shaders that use it

[bsalomon, 2011-09-14 17:32:20]

Chrome started enforcing that the GL_OES_shader_derivatives extension be enabled
in the shader. We (read as "I") were being lazy and not enabling it.

[TomH, 2011-09-14 17:56:25]

LGTM

[bsalomon, 2011-09-15 13:18:30]

Closed with r2269.