Currently, getopt bases its decision of whether to print "illegal option" or "invalid option" solely on the presence of POSIXLY_CORRECT, but POSIX 2001 relaxed the requirements so that the error message no longer need use the term "illegal". Is it worth updating the getopt module to depend on posixver and avoid this term except when _POSIX2_VERSION is set to the older version of POSIX?
-- Eric Blake
