Include long-options.h.

Include long-options.h.
[long_opts]: Remove.
(usage): Tweak --help output; use *_OPTION_DESCRIPTION macros.
(main): Don't use getopt directly.  Use parse_long_options instead.
Tweak a diagnostic.
Use EXIT_FAILURE rather than a literal `1'.
(main): If POSIXLY_CORRECT is set, don't recognize --help or --version,
so the program can operate on a file with one of those names.