_PyUnicode_AsString() raises an exception on unencodable filename.

The code is based on strncmp() of the libiberty library,
function in the public domain.

than TypeError raised by the iterator argument.  Also added a test to
check that zip() already behaves similarly.

Use test.support and unittest features.  Fix duplicated test (bad merge in r79033).  Fix comment for issue #7902.

zipimport is now able to load a module with an unencodable filename.

Write a message formatted by PyUnicode_FromFormatV() to sys.stdout and
sys.stderr.

Some of these are genuine bugs with objects bigger than 2GB, but
my system doesn't allow me to write tests for it.