Updated for ruby-2.0.0-rc1

RTEST is now a bare expression:

Thu Dec 20 18:29:54 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>

        * include/ruby/ruby.h (RTEST, NIL_P): make bare expressions without
          outermost parentheses.
NIL_P no longer includes wrapping parens either
Merge pull request #34 from nearbuy/ruby-2.0.0-rc1

Updated for ruby-2.0.0-rc1