docs: List new extensions added in Mesa 9.1

I did not list the *_get_program_binary extensions since they're not
useful to anyone with their current implementation (that supports 0
binary formats).

docs/relnotes-9.1.html

@@ -44,9 +44,16 @@ Note: some of the new features are only available with certain drivers.
 </p>
 
 <ul>
+<li>GL_ANGLE_texture_compression_dxt3</li>
+<li>GL_ANGLE_texture_compression_dxt5</li>
+<li>GL_ARB_ES3_compatibility</li>
+<li>GL_ARB_internalformat_query</li>
 <li>GL_ARB_map_buffer_alignment</li>
-<li>GL_ARB_texture_cube_map_array</li>
+<li>GL_ARB_shading_language_packing</li>
 <li>GL_ARB_texture_buffer_object_rgb32</li>
+<li>GL_ARB_texture_cube_map_array</li>
+<li>GL_EXT_color_buffer_float</li>
+<li>GL_OES_depth_texture_cube_map</li>
 </ul>