Improve exception message raised by PyFloat_AsDouble if the object does not have a nb_float slot.  This matches what PyInt_AsLong does.
Improve exception message raised by PyFloat_AsDouble if the object does not
have a nb_float slot.  This matches what PyInt_AsLong does.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator