resample with period='m' does not work on localized indexes for multiple methods in "how"
For the following code:

```
rng = pd.date_range('1/1/2011', periods=200, freq='D')
rng = rng.tz_localize('UTC')
ts = pd.Series(cumsum(randn(len(rng))), index=rng)
```

the following resample:
`ts.resample('m', how='mean')`
works fine, but this one:
`ts.resample('m', how={'Mean': 'mean', 'Std': 'std'})`
fails with the error: `TypeError: can't compare offset-naive and offset-aware datetimes`

However if we choose other interval of resampling (e.g. daily or quarterly or weekly):
`ts.resample('D', how={'Mean': 'mean', 'Std': 'std'})`
or
`ts.resample('Q', how={'Mean': 'mean', 'Std': 'std'})`
there would be no error.

OS: OSX 10.8.3
python: 2.7.4
pandas: 0.11.0
