PERF: Very slow clip performance
#### Code Sample, a copy-pastable example if possible

```python
In [38]: s = pd.Series(np.random.randn(30))

In [39]: timeit s.clip(0, 1)
100 loops, best of 3: 2.02 ms per loop
```

#### Problem description

There is more than 1000x performance difference between `Series.clip` and `numpy.clip`:

```
In [43]: timeit np.clip(arr, 0, 1)
1000000 loops, best of 3: 1.06 µs per loop
```

#### Output of ``pd.show_versions()``

pandas 0.19.2