dri: Flush the batch after a DRI swap/copy event

To minimise lag in those every so critical games, we want to ensure that
the copy happens as soon as it is received, so we need to flush the
batch after processing a swap event and before we go to sleep.

References: https://bugs.freedesktop.org/show_bug.cgi?id=37068
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/intel_dri.c

@@ -182,6 +182,8 @@ static PixmapPtr fixup_shadow(DrawablePtr drawable, PixmapPtr pixmap)
 	/* And redirect the pixmap to the new bo (for 3D). */
 	intel_set_pixmap_private(old, priv);
 	old->refcnt++;
+
+	intel_get_screen_private(xf86Screens[screen->myNum])->needs_flush = TRUE;
 	return old;
 }