i915tex: Fix triple buffering after recent Mesa core changes.

Remove superfluous _mesa_resize_framebuffer call which is now harmful because
it causes the third renderbuffer to have width/height 0, so Mesa refuses to
render to it.

In the long term, it would be nice to remove the hack in
intel_alloc_window_storage in favour of a proper Mesa interface for flipping
between more than two colour buffers.

src/mesa/drivers/dri/i915tex/intel_buffers.c

@@ -349,6 +349,28 @@ intelWindowMoved(struct intel_context *intel)
 
    /* Update Mesa's notion of window size */
    driUpdateFramebufferSize(ctx, dPriv);
+
+   /* Update size of third renderbuffer */
+   if (intel_fb->pf_num_pages == 3) {
+      struct gl_renderbuffer *rb = &intel_fb->color_rb[(intel_fb->pf_current_page
+						        + 2) % 3]->Base;
+
+      /* only resize if size is changing */
+         if (rb->Width != intel_fb->Base.Width ||
+	     rb->Height != intel_fb->Base.Height) {
+            /* could just as well pass rb->_ActualFormat here */
+            if (rb->AllocStorage(ctx, rb, rb->InternalFormat,
+				 intel_fb->Base.Width, intel_fb->Base.Height)) {
+               ASSERT(rb->Width == intel_fb->Base.Width);
+               ASSERT(rb->Height == intel_fb->Base.Height);
+            }
+            else {
+               _mesa_error(ctx, GL_OUT_OF_MEMORY, "Resizing framebuffer");
+               /* no return */
+            }
+         }
+   }
+
    intel_fb->Base.Initialized = GL_TRUE; /* XXX remove someday */
 
    /* Update hardware scissor */