divide does not work for Series of timedelta64[ns]
Using this Series:

```
In [38]: pd.Series([timedelta(1)])

Out[38]:
0   1 days, 00:00:00
dtype: timedelta64[ns]
```

This works: 

```
In [36]: pd.Series([timedelta(1)])[0]/ np.timedelta64(1,'D')

Out[36]:
1.0
```

But this does not:

```
In [39]:

pd.Series([timedelta(1)])/ np.timedelta64(1,'D')

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-39-753422ac6b07> in <module>()
----> 1 pd.Series([timedelta(1)])/ np.timedelta64(1,'D')

/usr/lib64/python2.7/site-packages/pandas/core/series.py in wrapper(self, other, name)
    128                 elif is_timedelta_lhs and name not in ['__add__','__sub__']:
    129                     raise TypeError("can only operate on a timedeltas for "
--> 130                                     "addition and subtraction, but the operator [%s] was passed" % name)
    131 
    132                 dtype = 'timedelta64[ns]'

TypeError: can only operate on a timedeltas for addition and subtraction, but the operator [__div__] was passed
```
