more hackish tests
workaround for numba #247 (nan should be != nan)
tweak integer division shield to not produce code that Numba can't handle.
Numba does not handle correctly "expr if 2 else 0" (it returns 0 instead of
expr), but to its defense, in a normal situation, it never sees code like that
since Python optimize the if clause away before Numba has a chance to see it.
more hackish tests