[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

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules.tmpl)