Do not run np.reciprocal for int16 due to inconsistent undefined numpy behavior

Numpy returns different values when converting a NaN to an int16 on 32 and 64-bit platforms.  The numpy docs do not seem to take a clear position, so for now skip this testing of np.reciprocal on int16 until we can implement all the required special cases.  (Note that the Numpy docs say that the reciprocal function "is not designed to work with integers.")