Limit the votes a user can cast in 24 hours

One of my clients (http://juice.altiris.com) is rewarding users for voting. Their hope was more people would read the articles and submit valid feedback and useful votes.

Well, a few users saw it as an easy way to click their way to free prizes by blindly voting on everything.

This patch includes code that allows the administrator to set a threshold number of votes (5, 10, 15 ...) a user can cast in 24 hours.

If the user exceeds the threshold, they see a message and are asked to try again later.

This is my first patch so please feel free to send me feedback if there are things I can do to improve.

Thanks!
Kevin