dri2: Event driven buffer validation.

When a buffer invalidation event is received from the X server, the
"invalidate" hook of the DRI2 flush extension is executed: A generic
implementation (dri2InvalidateDrawable) is provided that just bumps
the "pStamp" sequence number in __DRIdrawableRec.

For old servers not supporting buffer invalidation events, the
invalidate hook will be called before flushing the fake front/back
buffer (that's typically once per frame -- not a lot worse than the
situation we were in before).

No effort has been made on preserving backwards compatibility with
version 2 of the flush extension, but I think it's acceptable because
AFAIK no released stack is making use of it.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>

include/GL/internal/dri_interface.h

@@ -269,22 +269,20 @@ struct __DRItexBufferExtensionRec {
  * Used by drivers that implement DRI2
  */
 #define __DRI2_FLUSH "DRI2_Flush"
-#define __DRI2_FLUSH_VERSION 2
+#define __DRI2_FLUSH_VERSION 3
 struct __DRI2flushExtensionRec {
     __DRIextension base;
     void (*flush)(__DRIdrawable *drawable);
 
     /**
-     * Flush all rendering queue in the driver to the drm and
-     * invalidate all buffers.  The driver will call out to
-     * getBuffers/getBuffersWithFormat before it starts rendering
-     * again.
+     * Ask the driver to call getBuffers/getBuffersWithFormat before
+     * it starts rendering again.
      *
-     * \param drawable the drawable to flush and invalidate
+     * \param drawable the drawable to invalidate
      *
-     * \since 2
+     * \since 3
      */
-    void (*flushInvalidate)(__DRIdrawable *drawable);
+    void (*invalidate)(__DRIdrawable *drawable);
 };