Check if two files are identical with list(io.open()) rather then filecmp
    
    filecmp does the work fine but basically return a boolean while for the
    tests we are interested to know where the differences lay between the two
    files. So by moving the test to compare two lists, we can more easily
    see what are the differences between the two files.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>