IP Spoofing Check patch

I've added a patch to the "'IP spoofing attack' breaks with some
proxies" discussion.

http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/1200

The patch is a workaround to the issue, since the real problem is
poorly configured proxies, which can't be patched in Rails. Our site,
which has a lot of WAP traffic, generates massive amounts of false
positive "Spoofing Checks." To date, we've been monkey patching rails
to remove that check, but I think the change I've suggested is a
reasonable compromise.

Thanks,
Darren