resample error with closed='left' and label='right'.
``` python
from pandas import *

# ERROR
s = Series(0, index=date_range(start='1/1/2012 9:30', freq='1min', periods=21))
s.resample('10min', how='mean',closed='left', label='right')

# Works. Only changed the start time. 
s = Series(0, index=date_range(start='1/1/2012 9:31', freq='1min', periods=21))
s.resample('10min', how='mean',closed='left', label='right')
```

Happens whenever the binlabels are trimmed and the label is set to 'right'. It ends up reducing the labels twice. 
