Additional NumPy 1.8.0 warning fixes.

From building the documentation, I managed to find a few more deprecation warnings with NumPy 1.8.0.

There is one left over warning whose source I can't seem to find from `beamforming_fk_analysis_2.py`:
```
/usr/lib64/python2.7/site-packages/matplotlib/cbook.py:1711: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
  result = np.zeros(new_shape, a.dtype)
```
I'm not sure if maybe this is something in matplotlib that is triggered by one of the "future" imports that obspy uses.