Bounded and unbounded are not antonyms

It is currently possible to create a meaningless set of assumptions:

neither
```
    Dummy(zero=True, bounded=False) nor
    Dummy(zero=True, unbounded=True)
```
raise an error.

Further discussion is in the commit involving NaN.

- [ ] clean up S.in_Q discussion
- [x] change unbounded to infinite
- [ ] get good reference for definition of bounded (abs(x) < oo) and finite (0 < abs(x) < oo)
the old answer was confirmed numerically to be wrong and the new one "right" but neither agrees with WA which gives

```
(log(2/(m*(m-1))) + 2*I*pi*n)/log(2)
```