MAINT: Remove all mentions of unittest2.

[jvkersch]

Drive-by PR to remove all uses of unittest2, given that the lowest supported Python version is 2.7.

[jvkersch]

@itziakos Do you have any idea what might be going on here? This is the PR that I mentioned was getting killed during python setup.py develop. The Travis build log showed that this consistently happened during the enable build, more precisely while installing six. Manually doing pip install six before the enable build seems to fix the issue...

[corranwebster]

@jvkersch if six isn't already installed, then Enable's setup.py will probably try to install via easyinstall/setuptools (I think) rather than pip. So possibly some issue with setuptools and/or installing six via setuptools?

Enable has a rather nasty setup.py system, so it wouldn't shock me if there is something bad there.

[jvkersch]

That's possible. This is the line where it goes wrong in the build log:

Running six-1.10.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-ctwu5nzk/six-1.10.0/egg-dist-tmp-lic6svep

Shall we just add six to Enable's Travis requirements?

[corranwebster]

Yes.