Resampling sometimes returns an extra bin when closed left
```
print pandas.__version__
```

0.8.1

```
dtrange = pandas.date_range(start='1-1-2009', periods=31, freq='D')

raw = pandas.Series(np.arange(len(dtrange)), index=dtrange)
test1 = raw.resample('M', how='count', closed='left', label='left')
test2 = raw.resample('M', how='mean', closed='left', label='left')

print test1
```

2008-12-31    31

```
print test2
```

2008-12-31    15
2009-01-31     0
Freq: M

When closed on the right, the extra empty bin dissapears. Also note how it appears when resampling with a mean, but not when using count. 
