SimpleCaptcha 3 doesn't work with rails 3 RC

[rorra]

In rails 3 RC, the method valid? for an ActiveRecord object takes a parameter(context), so the captcha wasn't working because of it with rails 3 rc and ruby 1.9.2

I just made some small fixes to make it work.

Plus another person already took the work of updating the way to call old variables in rails that now belongs to the Rails module

Thank you so much for contributing with this captcha to the open source community :)