glsl: enable the new linear scan register allocator code

Seems to b working well enough to enable all the time.
Optimizations can be disabled with "export MESA_GLSL=nopt" if needed.
diff --git a/src/mesa/shader/prog_optimize.c b/src/mesa/shader/prog_optimize.c
index 458a69f..5f35dbf 100644
--- a/src/mesa/shader/prog_optimize.c
+++ b/src/mesa/shader/prog_optimize.c
@@ -803,11 +803,11 @@
    if (1)
       _mesa_remove_dead_code(program);
 
-   if (0) /* not test much yet */
+   if (0) /* not tested much yet */
       _mesa_remove_extra_moves(program);
 
-   if (1)
+   if (0)
       _mesa_consolidate_registers(program);
-   else /*NEW*/
+   else
       _mesa_reallocate_registers(program);
 }