Evaluate broken link checker plugin

[spelkey-ucd]

Here are requirements from Neil:

• Accurately identify broken links. Can we set it to deal with firewalls? The current checker seems to suffer from a lot of false positives.
• Push notifications to whoever we tell it - so either custom or by author of the affected page.
• Reliably check all of the links on the site.
• More sorting functionality - by "break found" date would be good, as well as by page view count over time.