Create a unit test config for the pub tests that's prettier.

In particular, it:

- Shows test results incrementally.
- Cleans up the stack traces.
- Doesn't show the failures and their stack traces twice.

Right now, it's opt in. You need to:
- Add initConfig() to the top of a test suite.
- Pass "--human" when you run the test.

At some point, I can add the initConfig() calls to every test suite but I figured we could just add them manually for now.

Review URL: https://codereview.chromium.org//11867012

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@17313 260f80e4-7a28-3924-810f-c04153c831b5