Fix GH-3: Wrap tests when they extend past line

This makes the checkmarks wrap on to another line when there are so many tests per file that the checkmarks would start hitting the progress bar.

Screenshot:

![pytest-sugar-fix-gh-3](https://f.cloud.github.com/assets/305268/2061526/2fc80ef8-8c58-11e3-9682-e229fd7b3945.png)

Fixes GH-3.

Cc: @Frozenball, @kevinburke, @sontek, @aconrad