Remove to_sym from condition creation

This prevents a DoS http://www.tricksonrails.com/2010/06/avoid-memory-leaks-in-ruby-rails-code-and-protect-against-denial-of-service/
Use public_send on condition creation

This makes sure you can't call Kernel methods like `throw`
Add history message
Merge pull request #273 from Shopify/make-if-less-dangerous

Make if less dangerous