texturing is not enabled, and without requiring the two colors be
added externally.
As a part of this, collapsed the decomposition of quads into triangles
inside swrast to be hardwired into _swrast_Quad; removed s_quads.[ch].
Removed checks on texture state from t_vb_light.c, which was previously
required by swrast.
Moved the t_dd_ templates to a new directory.
