def md5_file(path)
      File.open(path) do |f|
        digest, buf = Digest::MD5.new, ""
        while f.read(4096, buf)
          digest.update(buf)
        end
        digest.hexdigest
      end
    end
def md5_file(path)
      File.open(path) do |f|
        digest, buf = Digest::MD5.new, ""
        while f.read(4096, buf)
          digest.update(buf)
        end
        digest.hexdigest
      end
    end
Return the md5 checksum for the file at +path+.