Fix binding change after security patch

The security patch introduced a regression with the binding change from
the UI.
Merge pull request #63 from gsamokovarov/security-regression

Fix binding change after security patch
Introduce basic Rubinius support

This one didn't see the testing it deserved and can be implemented
better by using Rubinius internals, rather then this shaky
`binding_of_caller` frame guessing. For now, I wanna roll this out as a
experimental Rubinius support. We'll make it better post `2.0`.

I'm seeing gem installation errors on Travis at the moment, but the test
pass locally. If Travis continues to fail this days I'll allow failures
for Rubinius. I would like to avoid that.