Add support for multi-byte locales.

Add support for multi-byte locales.
(iswprint, mbrtowc, wcwidth): Provide default definitions.
(total_bytes): New variable.
(print_bytes): New variable.
(longopts): Change abbreviation for --chars from 'c' to 'm'.
(usage): Update.
(write_counts): Add `bytes' argument.
(wc): New variables `bytes', `count_bytes', `count_chars',
`count_complicated'. The old code determines `bytes', not `chars'.
New case for MB_CUR_MAX > 1. A non-printable non-space character does
not increment the line position or start a word. Update `total_bytes'.
(main): Initialize `print_bytes' and `total_bytes' to 0. Accept 'm'
option. Pass `total_bytes' to write_counts.