Resample BM adds extra index point

```
In [1]: index = pd.DatetimeIndex(start='20150101', end='20150331', freq='B')

In [2]: df = pd.DataFrame(index=index, data=len(index)*[0])

In [3]: df.resample('BM', how='last')
Out[3]:
             0
2015-01-30   0
2015-02-27   0
2015-03-31   0
2015-04-30 NaN
```

This is both in 0.14.1 and 0.15.2
