Python testing

[longjon]

After #1472.

This PR adds Python testing of very basic functionality.

• Testing is through the built-in unittest module. We might want to consider other testing libraries (like nose) in the future, but this is fine for now.
• Hooks are added for the Makefile (make pytest) and Travis.
• Tests are meant to exercise tricky things that come up in the Python wrapper (like memory management), and not be redundant with existing C++ tests.
• Only very basic testing (of some functions from _caffe) is included so far. I'm going to go ahead and work on pycaffe on top of this, but BVLC folk are welcome to push more tests to this branch, and decide whether this should be merged right away (to at least have some testing) or a bit later (so that testing is not misleading by its paucity).
• Includes a bugfix revealed by the tests.

[longjon]

And, Travis finally passes. Attempting to install the Python dependencies via pip was agonizingly slow, so I switched to using miniconda instead.

[jeffdonahue]

Awesome, looks good to me from my brief read through. This should definitely be merged before any other PyCaffe changes.

[tleyden]

Attempting to install the Python dependencies via pip was agonizingly slow, so I switched to using miniconda instead.

Yup, I've watched that in agonizing pain while building a docker image.

Can you post details of using miniconda?

[longjon]

@tleyden: see the diff, which is based on https://gist.github.com/dan-blanchard/7045057 plus trial and error, and also this more official looking page: http://conda.pydata.org/docs/travis.html.

[shelhamer]

Needs update from merge of #1472.

[longjon]

@shelhamer rebased.

[longjon]

To facilitate easier merging, I moved the bug fix that was here to #1228.

[longjon]

Haha, oops, I was testing for that bug fix. I'll leave this as it is for now, and either #1228 will be merged and I'll rebase, or I'll push the fix to dev at some point and rebase, or something.

[longjon]

Rebased after #1228 and passing again.