TST: fix thousands of deprecation warnings during tests with numpy 1.8 on Python 3

E.g. `partsort_test.py:47: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future`
Merge pull request #73 from cgohlke/patch-1

TST: fix thousands of deprecation warnings during tests with numpy 1.8 ...