Fix test_sys for FreeBSD, Solaris and Mac OS X
Fix test_sys for FreeBSD, Solaris and Mac OS X

_Py_char2wchar() (mbctowcs) decodes b'\xff' to '\xff' on FreeBSD, Solaris and
Mac OS X, even if the locale is C (and the locale encoding is ASCII). Patch
test_undecodable_code() to support this output and document the two different
kinds of outputs.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator