mesa: add fbo/texture support for ARB_texture_cube_map_array (v2)

This adds the mesa core + texture + fbo support for the
texture cube map array extension.

v2:
add comment to _mesa_num_tex_faces related to cube map arrays (Brian)
drop wrong comment cut-n-paste (Brian)
fix / 6 maximum check issue (Kenneth)
coalsece some array case statements (Kenneth)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/mesa/main/shared.c

@@ -90,6 +90,7 @@ _mesa_alloc_shared_state(struct gl_context *ctx)
    for (i = 0; i < NUM_TEXTURE_TARGETS; i++) {
       /* NOTE: the order of these enums matches the TEXTURE_x_INDEX values */
       static const GLenum targets[] = {
+         GL_TEXTURE_CUBE_MAP_ARRAY,
          GL_TEXTURE_BUFFER,
          GL_TEXTURE_2D_ARRAY_EXT,
          GL_TEXTURE_1D_ARRAY_EXT,