[FIX JENKINS-19250] Add causes to queue item tool tip

One cause:
> ![screen shot 2014-05-21 at 21 51 34](https://cloud.githubusercontent.com/assets/1831569/3045952/25bde8ae-e123-11e3-80a6-f43eb7d916e2.png)

Multiple causes:
> ![screen shot 2014-05-21 at 21 52 35](https://cloud.githubusercontent.com/assets/1831569/3045953/26ee7374-e123-11e3-9dd9-e540bb734045.png)