Split apart unit tests

[paulirish]

It's nice to just run a few unit tests at once instead of waiting for all 40 to finish. Plus this is more manageable, regardless.

No functional changes made. The test_helper/index file (https://github.com/paulirish/git-open/commit/f80f7ba2d6d07bd4e0198b4ab7e13cd1f4493008) is the most interesting part of this commit. And it's quite dull.

This does change the order the tests run in.

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Merging note: do not squash. I wrestled with git to make sure we have blame history on these files. :)

[paulirish]

Guh, I wish i did this post- #109. Oh well.

I'll do the rebase dance for this after #109 and #114