[entity] comparing two entities returns NotImplemented Fixes a test when using some versions of unittest2, where assertItemsEqual tries a sort and expects TypeError, which it doesn't get if we directly raise NotImplementedError. The NotImplemented value is treated specially by the interpreter: https://docs.python.org/3.4/library/constants.html#NotImplemented

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"""cubicweb-%(cubename)s application package

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%(longdesc)s

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"""