Reuse beautiful formatting when showing error summaries

If you have lined up your error messages to be easy to scan visually when a test fails, the summary at the end breaks this formatting, on behalf of not reusing the normal error formatting code.

Example screenshot from before this change:

![before](https://f.cloud.github.com/assets/2459/607425/221c7e84-cd44-11e2-89a9-5f8787270323.png)

After:

![after](https://f.cloud.github.com/assets/2459/607428/283697fa-cd44-11e2-9b71-c20df118e2c5.png)