Properly handle unit tests on reload.

Check for the correct folder to determine if unit tests are installed. If they are installed, perform svn up instead of displaying "already installed" message.
Setup unit tests from the "trunk" WordPress install.

It is best to do unit testing against trunk. Ideally, I wanted to be able to flexibly test against trunk or latest stable. This is going to take some tinkering to get right, so, for now, unit tests will be run against the trunk install.