Convert docstrings to comments for nose; PEP8 cleanup (some tests activated)
Small further cleanups of ma.tests, plus correction for python3
One revert (comparisons with None; not PEP8, but good to check); extra comments
MAINT: update runtests.py from scipy

The additional chdir before starting the test allows tests that launch
subprocesses to run.

Fixes gh-3909
Merge pull request #3910 from pv/runtests-fix

MAINT: update runtests.py from scipy
Merge pull request #3906 from mhvk/ma/test-pep8-and-cleanup

Convert docstrings to comments for nose; PEP8 cleanup (some tests activated)