draw: account for separate shader objects in geometry shader code

draw: account for separate shader objects in geometry shader code

The geometry shader code seems to have been originally written with the
assumptions that there are the same number of VS outputs as GS outputs and
that VS outputs are in the same order as their corresponding GS inputs. Since
TGSI uses separate shader objects, these are both wrong assumptions. This
was causing several valid vertex/geometry shader combinations to either render
incorrectly or trigger an assertion.

Conflicts:
	src/gallium/auxiliary/draw/draw_gs.c

Reviewed-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: José Fonseca <jfonseca@vmware.com>