TST/BUG: fix 2to3 import rewrite of import pickle
In pandas.io.pickle the following statement will not allow python to import 
anything due to the following rewrite by 2to3

import pickle -> from . import pickle

This makes the import try to import itself ad infinitum and thus fails.

closes #4062

@jreback even though i said 0.13 for this one i'd like to get this in for 0.12 would be nice to be able to run tox on py3.x...
 ok by me
 btw i tried w/ numpy 1.5.1 and works fine
 I think it's time to ditch tox_prll.sh and move to [detox](https://pypi.python.org/pypi/detox), 
tox_prll was a hack from a time when detox was having growing pains. 
 is this a dropin replacement?
