Add GL_ARB_texture_cube_map support for i830. Most of the code was

Add GL_ARB_texture_cube_map support for i830.  Most of the code was
lifted from the i915 side.  i830 will now report version 1.3!  Hurrah!
With the exception of GL_EXT_texture_compression_s3tc, the i830 driver
now supports all the extensions that its Windows counterpart supports.