This allows py.test to run the test suite

There are two main python test runners: nosetests and py.test. We use
nosetests in `make test` but py.test is nicer and we should probably
switch to it (we talked about this a while ago). This small commit makes
the suite pass under py.test.
Merge branch 'fix-for-py.test' into fix-merge-again
Fix test that I broke with the #1462 fix