TST + PY3 various fixes

* Little hack in fixes.py that can be removed when NumPy's
  https://github.com/numpy/numpy/issues/3484 is fixed.
* Little cleanup to the fixes implementation.
* Change the numpy workaround and added a test. Fixed some xrange usage.
* Fix the weight boosting test.
* None is not comparable in python3
* Fix a test that depended on dictionary iteration order.
* Python3 removed execfile
* More test fixes.

Fixes #2122.