Convert bundler's Gemfile into Heroku's .gems

heroku-gemfile.rb

def disable_rubygems; nil; end
def source(s); $src = s unless s[/gemcutter/] end
def gem(n, v)
  if Hash === v
    $stderr.puts "ignoring git gem #{n}"
    return
  end
  puts "#{n} -v#{v}#{$src ? " -s#{$src}": ""}"
end
load ARGV[0] || "Gemfile"