The CSO returned by pipe->create_vs_state() can't be passed to the
private draw module. That was causing glRasterPos to blow up.
Add a 'draw_shader' field to st_vertex_program for use with the private
draw module.
Change st_context->state.vs type from cso_vertex_shader to st_vertex_program.
We were doing this for the sake of softpipe and the tgsi intergrepter since
we always need the fragment position and W-coordinate information in order
to compute fragment interpolants.
But that's not appropriate for hardware drivers.
The tgsi interpreter now get x,y,w information from a separate tgsi_exec_vector
variable setup by softpipe.
The new pipe_shader_state->input_map[] defines how vert shader outputs map
to frag shader inputs. It may go away though, since one can also examine
the semantic label on frag shader input[0] to figure things out.
