BUG: _coerce_to_dtypes: Timestamp is not defined.
@jreback - `Timestamp` isn't actually defined/imported in core/common. Did you mean `lib.Timestamp`?

``` python
# snippet from core/common.py
def _coerce_to_dtypes(result, dtypes):
    """ given a dtypes and a result set, coerce the result elements to the dtypes """
    if len(result) != len(dtypes):
        raise AssertionError("_coerce_to_dtypes requires equal len arrays")

    def conv(r,dtype):
        try:
            if isnull(r):
                pass
            elif dtype == _NS_DTYPE:
                r = Timestamp(r)
            elif dtype == _TD_DTYPE:
                r = _coerce_scalar_to_timedelta_type(r)
            elif dtype == np.bool_:
                r = bool(r)
            elif dtype.kind == 'f':
                r = float(r)
            elif dtype.kind == 'i':
                r = int(r)
        except:
            pass

        return r

    return np.array([ conv(r,dtype) for r, dtype in zip(result,dtypes) ])
```
