Windows compatibility (with Future Absolute Imports)

This is a cleaner re-attempt of #97, but it's not _quite_ complete -- I'm afraid this is closer to code-review than pull-request.

Notes:

1. `python setup.py test` is [throwing a new error for me right now](https://ci.appveyor.com/project/edbrannin/mkdocs/build/0.9.0.13), on Linux and Windows.
2. `./runtests` is having an absolute-import problem (via `coverage`).
  - In #97 I solved this by pulling `mkdocs/test.py` out to the root (next to `setup.py`).  Does this seem reasonable to you?
3. I haven't re-integrated [this fix to test_config_option](https://github.com/edbrannin/mkdocs/commit/bf1f68f29bb9b3065c20ac7169f4a59be02e5809) yet because:
  - The patch-reapply failed on master and I don't have time to fix it just yet
  - I think it would be better to attempt the above fix with a context manager
4. This is a new PR with brand-new patched-and-reapplied changes mainly because I'm not super-comfortable with git rebasing yet.  I hope it's not any trouble.