DateTimeIndex displayed incorrectly.
I am using the latest pandas from git and numpy 1.7.0-dev.  See Out [27] below:

```
In [25]: df = pandas.DataFrame({'t': [datetime.datetime.now()], 'x': [0]}).set_index('t')

In [26]: df
Out[26]: 
                            x
t                            
2012-07-17 09:18:21.993665  0

In [27]: df.index
Out[27]: 
<class 'pandas.tseries.index.DatetimeIndex'>
[1840-03-20 01:03:32.867732032]
Length: 1, Freq: None, Timezone: None

In [28]: df.index.asi8
Out[28]: array([1342516701993665000])
```

Edit: It's worse with datetime64.

```
In [31]: df = pandas.DataFrame({'t': [np.datetime64(datetime.datetime.now())], 'x': [0]}).set_index('t')

In [32]: df
Out[32]: 
                            x
t                            
1840-03-23 05:51:57.596732  0

In [33]: df.index
Out[33]: 
<class 'pandas.tseries.index.DatetimeIndex'>
[1964-11-16 11:52:40.252490752]
Length: 1, Freq: None, Timezone: None

In [34]: df.index.asi8
Out[34]: array([-4095338882403267968])
```
