Removed Ruby warnings

Removed some Ruby warnings. Though I couldn't test them, so beware.

Also, I found two cases where I'm unsure about:
- /home/tobias/.rvm/gems/ruby-2.0.0-p0/gems/therubyracer-0.11.4/lib/v8/init.so: warning: method redefined; discarding old IntegerValue
- The whole code line not needed? https://github.com/cowboyd/therubyracer/blob/0c8ab86dc15ff8e1637920c790412dd4991b3598/lib/v8/error.rb#L43