Float Index Interpreted as Object dtype
When I cast a FloatIndex to a numpy array, I get an array of objects.  The desired behavior should be float.  This is backwards incompatible with pre-FloatIndex behavior.  

``` python
In [119]:   s = pd.Series([1,2,3],[1.,2.,3.])
               array(s.index).dtype

Out[119]:  dtype('O')
```

The Int64Index works as expected.

``` python
In [114]:    s = pd.Series([1,2,3],[1,2,3])
                array(s.index).dtype

Out[114]:  dtype('int64')
```
