Adding != operator to list of binary operators

Ruby2Ruby writes `!=` as a method call, eg: `1.!=2`.  This pull request fixes this by treating `!=` as a binary operator instead: `(1 != 2)`.  Ordinarily this wouldn't be an issue (operator method calls work fine in Ruby 1.9/2.0), but I'm currently working on generating code that has to be compatible with Ruby 1.8 as well.