Add completion time to test run output.

When leaving ```lein midje :autotest``` running in the background, it's not always clear whether tests have been run after making changes (especially if they've been passing). This branch adds a message to the test output so that the execution time is easily viewable.
![screen shot 2013-09-29 at 3 49 09 pm](https://f.cloud.github.com/assets/636796/1233740/4eb00120-2940-11e3-8e20-de849806f9b4.png)