hash the contents of the public directory, inspired by http://grosser.it/2010/01/12/checksum-for-a-whole-folder-in-ruby/

gistfile1.rb

  def self.commit_hash
    @commit_hash ||= begin
      files = Dir["public/**/*"].select { |f| File.file?(f) }.sort
      contents = files.map { |f| File.read(f) }.join
      hash = Digest::MD5.hexdigest(contents)[0..6]
      "rel-#{hash}"
    end
  end