Gem upgrade, removed ActiveSupport::CoreExtensions.

It looks like ActiveSupport was completely refactored to get rid of those extension modules, all the methods in `core_ext` are just declared on the opened up classes. This makes `sandboxed_erb` load with an error: "undefined class ActiveSupport::CoreExtensions".  I think the right thing to do is to get rid of the custom code that deals with this.

Other gem upgrades here too that make all tests pass.