draw: Add GALLIUM_DUMP_VS environment variable.

Add GALLIUM_DUMP_VS to dump the vertex shader to the console like
GALLIUM_DUMP_FS in softpipe.
diff --git a/src/gallium/auxiliary/draw/draw_private.h b/src/gallium/auxiliary/draw/draw_private.h
index 2a11b8c..d5e1c0c 100644
--- a/src/gallium/auxiliary/draw/draw_private.h
+++ b/src/gallium/auxiliary/draw/draw_private.h
@@ -172,6 +172,8 @@
 
    boolean force_passthrough; /**< never clip or shade */
 
+   boolean dump_vs;
+
    double mrd;  /**< minimum resolvable depth value, for polygon offset */
 
    /* pipe state that we need: */
diff --git a/src/gallium/auxiliary/draw/draw_vs.c b/src/gallium/auxiliary/draw/draw_vs.c
index 3553689..60b4dd9 100644
--- a/src/gallium/auxiliary/draw/draw_vs.c
+++ b/src/gallium/auxiliary/draw/draw_vs.c
@@ -83,6 +83,10 @@
 {
    struct draw_vertex_shader *vs;
 
+   if (draw->dump_vs) {
+      tgsi_dump(shader->tokens, 0);
+   }
+
    vs = draw_create_vs_llvm( draw, shader );
    if (!vs) {
       vs = draw_create_vs_sse( draw, shader );
@@ -152,6 +156,8 @@
 boolean 
 draw_vs_init( struct draw_context *draw )
 {
+   draw->dump_vs = debug_get_bool_option("GALLIUM_DUMP_VS", FALSE);
+
    draw->vs.machine = tgsi_exec_machine_create();
    if (!draw->vs.machine)
       return FALSE;