Finish the backend part of : Ban IPs of anonymous spammers for 6 hours (task #4141).

(Browse SVN revision 6356)

Considering the ban is non-blocker (someone can create an account, log in and continue to work), I think acceptable to extend it to 6 hours.

• we'll search for items flagged in the last 6 hours
• we'll apply a ban for the next 6 hours, starting from the time of the actual flagging

It means that in total, there can be 12 hours between the time the content was posted and the time when the ban ends. But still, no more than 6 hours ban.

After some talks with Yves, we concluded it would be a good move to ban IP of users that sent spams in the last 3 hours.

Yves noticed some patterns in the way spams are posted, and if a spam get caught soon enough, it we could then avoid further spams coming from the same source in the next coming hours.

A 3 hours ban is not a big drama.

This wont affect authenticated users, it wont disallow authentication or account creation (unlike dnsbl checks).

So it means that if someone feels that it has been banned by mistake, he can easily workaround the problem by logging-in.
The site admin will have the possibility to remove the ban.

This should be easy to implement. It just requires to register the IP of any anonymously added content.

sv_cleaner will be in charge of removing banned IP after three hours (we wont keep IP banned forever because we dont want to deal with problems due to dynamic IPs)