BUG: boxing Timedeltas on .apply
Consider the following Series:

```
object_id
0CKVYKjyFn    76 days
0CrPL2QKH3   -15 days
0CrVStlVrg    23 days
0Cc5ZvS67u    76 days
0CTOk5OdtI    76 days
0CTSWtTzBa    76 days
0CwBqVeNCX    76 days
0CIRJFIOcD    58 days
0CRQPCxzQe   350 days
0CAq4m9Nru    15 days
0C617yvXBj    76 days
0CzUUJNKX9   -16 days
Name: days_left, dtype: timedelta64[ns]
```

I am hoping to convert the above to hours. 

If I do:

```
my_series.dt.hours
```

I get:

```
AttributeError: 'Series' object has no attribute 'hours
```

What's even more strange is that if I do:

``` python
> my_series[0].total_seconds()/3600
1824.0
```

it works for one element, but if I do:

```
> my_series.apply(lambda x: x.total_seconds())
```

I get:

```
AttributeError: 'numpy.timedelta64' object has no attribute 'total_seconds'
```

I thought `apply` would run the function I pass it item by item in the series. Why does `total_seconds()` work for a single item, but not with `apply`?
