Handle other unit types in datetime64 scalar objects
```
In [4]: val
Out[4]: 2012-02-05 00:00:00

In [5]: type(val)
Out[5]: numpy.datetime64

In [6]: val.dtype
Out[6]: dtype('datetime64[D]')

In [7]: DatetimeIndex([val])
Out[7]: 
<class 'pandas.tseries.index.DatetimeIndex'>
[1970-01-01 00:00:00.000015375, ..., 1970-01-01 00:00:00.000015375]
Length: 1, Freq: None, Timezone: None
```
