friendlier setup.py errors when numpy is missing.
(I have a patch for this coming in, see if you like where it goes)

issues:

1)  need numpy for dependency compilation
2)  no easy way to tell `setup.py` to get `numpy` and work with it first.  (or is there?)
3)  `$ pip install numpy pandas` still isn't enough.  

So the best I can do I give a friendlier message.  Patch inbound.
