datetime to index issue
I'm not sure if this is related to the datetime64 issues listed I've seen posted here. Still haven't really figured out exactly what is going but the date gets mangled when it moved to an index.

```
In [93]: import datetime, pandas
In [94]: df = pandas.DataFrame([[datetime.datetime.today(), 12.1]], columns=['Date', 'Value'])

In [95]: df = df.set_index('Date')

In [96]: df
Out[96]: 
                            Value
Date                             
2012-11-22 12:12:40.905739   12.1    

In [97]: df.index
Out[97]: 
<class 'pandas.tseries.index.DatetimeIndex'>
[2190-12-31 02:18:44.941732032]
Length: 1, Freq: None, Timezone: None

In [98]: df = df.reset_index()

In [99]: df
Out[99]: 
                           Date  Value
0 2190-12-31 02:18:44.941732032   12.1
```
