Bug 1032371 - Display users who have completed task on task detail page

Thanks for addressing the comma issue, @tessie. There are still a couple of issues with the appearance though.

1. There is now a space between the user's name and the comma. The comma should immediately follow the user's name without a space. There should still be a space *after* the comma though.
2. There is not enough room at the bottom of the page between the list of users and the buttons. See the attached screenshot for an example.

![screenshot 2014-12-04 09 17 55](https://cloud.githubusercontent.com/assets/142755/5302602/c8855ba4-7b96-11e4-9720-ddb1a49489dc.png)

Also, when you are adding a commit which addresses comments in a pull request, please add a comment to the commit message that describes the changes you are committing and why. This makes the code review process easier.