Install bundler & rake if it don't installed on system

Few bash functions use ruby libraries rake and bundler. I got error message when try to install rbx with ruby 2.0.0 which don't have `bundler` gem. Also I review possible issue with rake. First before calling this command we should check if it exists. Also if project uses bundler calling rake command without "bundle exec" may through exception of different versions of used and specified in Gemfile. That why I add two methods - safe_bundle & safe_rake which prevent mentioned cases.