Python 3 directly decodes the text when it is read(). If there is any
invalid UTF-8 character in the text an exception is thrown (IIRC it is
UnicodeDecodeError). Opening the file with `error='ignore'` avoids
throwing an exception and just ignores the invalid character. Since
this is only possible since Python version 3 there must be extra code
for older versions.
The test script has been enhanced. It now also uses a package which
contains a file with at least one invalid UTF-8 character.
8c32cfe853