i965: Add an INTEL_DEBUG=reemit option.

Jason and I use this for debugging all the time.  Recompiling the driver
to enable it is kind of annoying.  It's a great thing to try along with
always_flush_batch=true and always_flush_cache=true to detect a class of
problems - namely, atoms listening to an insufficient set of dirty bits.

Reviewed-by: Matt Turner <mattst88@gmail.com>

docs/envvars.html

@@ -192,6 +192,7 @@ See the <a href="xlibdriver.html">Xlib software driver page</a> for details.
    <li>perfmon - emit messages about AMD_performance_monitor</li>
    <li>pix - emit messages about pixel operations</li>
    <li>prim - emit messages about drawing primitives</li>
+   <li>reemit - mark all state dirty on each draw call</li>
    <li>sf - emit messages about the strips &amp; fans unit (for old gens, includes the SF program)</li>
    <li>shader_time - record how much GPU time is spent in each shader</li>
    <li>spill_fs - force spilling of all registers in the scalar backend (useful to debug spilling code)</li>