newey west weight is always 0
In the `newey_west` function in `pandas.stats.math`, the weight variable is always gonna be 0, since max_lags and lag are both integers and lag < max_lags+1. So the newey-west lag has no effect on the Xeps. Is that right?

```
    Xeps = np.dot(m.T, m)
    for lag in range(1, max_lags + 1):
        auto_cov = np.dot(m[:-lag].T, m[lag:])
        weight = lag / (max_lags + 1)
        if nw_overlap:
            weight = 0
        bb = auto_cov + auto_cov.T
        dd = (1 - weight) * bb
        Xeps += dd
    Xeps *= nobs / (nobs - df)
```
