def compare_file(a, b)
    return false unless File.size(a) == File.size(b)
    File.open(a, 'rb') {|fa|
      File.open(b, 'rb') {|fb|
        return compare_stream(fa, fb)
      }
    }
  end
Returns true if the contents of a file A and a file B are identical.

FileUtils.compare_file('somefile', 'somefile')  #=> true
FileUtils.compare_file('/bin/cp', '/bin/mv')    #=> maybe false