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Triggering assertions (pickle) and producing incorrect output
(cPickle) are certainly bugs, and being able to pickle a
recursive structure is not a feature request. The copy_reg
part of the patch is the real fix, and as it's almost a
translation of what reduce_2 already does, it should be safe
for 2.4. I agree that the rest of the patch--to check for
cycles during pickling--should wait until 2.5.