BUG: Make numpy import when run with Python flag '-OO'.

This consists of checking for a docstring equal to None and skipping two
tests that require docstrings.

Closes #5148.
TST: Add test with python flag -OO.
Merge pull request #5149 from charris/fix-ma-docs-for-OO-option

BUG: Make numpy import when run with Python flag '-OO