od: standard -s option

[mknos]

• Standards document outlines the -s flag is intended for 2-byte signed decimal display [1]
• OpenBSD, FreeBSD, GNU and Solaris support this meaning of -s [2]
• The -i flag already follows OpenBSD and prints 2-byte signed decimal, so make -s equivalent to -i
• NB: FreeBSD and GNU treat -i as decimal-of-size-int instead of decimal-of-two-bytes, but -i is not standardised

1. https://pubs.opengroup.org/onlinepubs/009696899/utilities/od.html
2. https://shrubbery.net/solaris9ab/SUNWaman/hman1/od.1.html

[briandfoy]

changes: add -s option and make it the same as -I (two byte signed decimal display)