Add more support for POSIX 1003.1-2001, which requires removal for

Add more support for POSIX 1003.1-2001, which requires removal for
support of obsolete "-N" option syntax in expand, head, fold,
split, tail, unexpand, uniq, and which prohibits options with
optional arguments in od and pr.

(usage): Document it.
(main): Check for obsolete options.
(short_options): New constant.
(SEP_STRING_OPTION): New enum value.
(long_options): Use it.