(gid_to_chars, major_to_chars, minor_to_chars)

(mode_to_chars, off_to_chars, size_to_chars, time_to_chars)
(uid_to_chars, uintmax_to_chars): Return bool
(to_chars): Return bool
(start_header): Check return values of convertion routines. Fail
if unable to store data in the header.