This will keep copyrect rendering actions in order with tight and tightPNG
rendering actions (otherwise you can get visual image corruption when
they are mixed together).
Warning:
RAW, RRE and HEXTILE still use immediate render commands so there is
still the risk of out-of-order rendering if RAW, RRE, and HEXTILE are
mixed with tight and tightPNG. Copyrect will work with either because
the renderQ_push function will render copyrects immediately if they
are the only thing being pushed on the queue.
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