Fix for Python 2.3 compatibility.
Note: Name of comparing function of sort() is "cmpfunc" in Python 2.3
and "cmp" in Python 2.4.
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory