MFC r212244: printf(1): Clarify that \OOO produces a byte, different %b

MFC r212244: printf(1): Clarify that \OOO produces a byte, different %b
escape sequences.

Octal escape sequences are expanded to bytes, not characters, and multiple
are required for a multibyte character.

The valid escape sequences in %b strings are slightly different from the
escape sequences in the format string.

git-svn-id: svn://svn.freebsd.org/base/stable/8@221017 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f