Several changes for POSIX and FreeBSD compatibility.

Several changes for POSIX and FreeBSD compatibility.
(COMMON_SHORT_OPTIONS): Add -B, -D, -e, -F, -H, -I, -L, -O, -s, -X.
(long_options, main): --strings is now -S, not -s.
(usage): Reflect the usage changes.
(parse_old_offset): Do not issue a diagnostic on failure;
callers now do this as necessary.
(main): Support POSIX syntax.  Remove unused case 0 from getopt_long.
Add support for new short options (many undocumented) for
compatibility with FreeBSD.  Remove FIXME for -s; it's now
POSIX-compatible.  Default format is now oS, not o2.