Combined commits: fix a minor issue with np.nansum behavior changing
from 1.8-1.9
add numpy 1.8 nanfunctions to ensure np1.8 = np1.9 behavior

udpate tests

moments no longer uses np.nansum (np_compat.nansum instead)

remove all but nansum, nanmin, nanmax

import things that needed to be imported (oops)

correct imports and add support functions for numpy 1.7.  If this fails
on 1.6, 3.2, I suggest we drop support for them

completely copying over numpy functions was way too much and would have
lead to a huge maintenance burden.  Instead, just overload nansum and
leave the rest untouched

remove np_compat; we're just going to change the tests

remove np_compat

1.9 nanish override; everything else gets to stay the same
separate concerns as per @ChrisBeaumont's suggestion
Merge pull request #150 from keflavich/np18nan

numpy 1.8 compatibility for NAN functions