Resample bug after converting tz
```
dr = date_range(start='2012-4-13', end='2012-5-1')
ts = Series(range(len(dr)), dr)
ts_utc = ts.tz_convert('UTC')
ts_local = ts_utc.tz_convert('America/Los_Angeles')
ts_local.resample('W')
```

yields

``` traceback
~/env/lib/python2.7/site-packages/pandas/tseries/resample.pyc in _get_time_bins(self, axis)
    107 
    108         # general version, knowing nothing about relative frequencies

--> 109         bins = lib.generate_bins_dt64(axis.asi8, binner.asi8, self.closed)
    110 
    111         if self.label == 'right':

~/env/lib/python2.7/site-packages/pandas/lib.so in pandas.lib.generate_bins_dt64 (pandas/src/tseries.c:60938)()

ValueError: Values falls before first bin
```
