Add translation for 'Anonymous' author

When a comment author is removed he is shown as 'Anonymous' without
options for translation.

Fix #2563:

![screen shot 2013-10-13 at 5 58 28 pm](https://f.cloud.github.com/assets/379894/1322787/3ba266c6-344a-11e3-9e3a-92519da367fa.png)