bad firms: add monitorengine.com to the list

The monitorengine.com domain is used by Panopta, which is a firm that
re-sells monitoring service. Interestingly enough, on their own
website they admit that if you see the check it might be because

  "A  competitor might be looking for comparison data on their online presence"

So basically they allow anybody to ping your websites without
validating where the request comes from to begin with. Even though
it's just HEAD requests, they also insist quite a bit, as it repeats
every 15 minutes.

Until they change their company line, I don't want to deal with them.