Fix bug summary sanitization (1030401 and 1030959)

The angular sanitize module was failing because some bug summaries
contain unclosed tags. I added a filter to escape '<' and '>' characters
before the word highlighter filter. This fixes both bug 1030401 and
1030959
Merge pull request #97 from mozilla/bug-1030401

Fix bug summary sanitization (1030401 and 1030959)