dt.view results in an AttributeError... can't figure out why.
```
>>> from pandas import date_range
>>> dt = date_range('2013-1-1', periods=100)
>>> dt.view('i8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/arjan/tmp/git/pandas-agijsberts/pandas/core/index.py", line 190, in view
    result = super(Index, self).view(*args, **kwargs)
AttributeError: can't set attribute
```
dt.values.view('i8') instead works as expected, but I'd assume that also dt.view('i8') should work.