Remove posixver.h and its uses.

Remove posixver.h and its uses.
(obsolete_usage): Remove.
(join_field_1, join_field_2): Initialize to SIZE_MAX to indicate
they haven't been set yet.
(tab): Now int, not char.  Initialize to -1 to indicate white space
separates columns, so that we can use NUL as a separator.
All uses changed.
(OBSOLETE_LONG_OPTIONS, get_option): Remove.
(string_to_join_field): Remove ERR_MSG_FMT arg; a single format
suffices.  Use xstrtoul for sizes; it suffices.
(decode_field_spec): Report an error and exit on failure.  Return void,
not bool.
(add_field_list): Likewise.
(set_join_field): New function.
(enum operand_status): New enum.
(add_file_name): New args OPERAND_STATUS, JOPTION_COUNT,
PREV_OPTC_STATUS, OPTC_STATUS to handle the bewildering array of
possibilities with obsolete option parsing.
(main): Use it.  Do not depend on POSIX version.
Check for conflicting options.  Parse obsolete options -j1 and -j2
so that it is a pure extension to POSIX 1003.1-2001.
Allow '-t\0' to specify a NUL tab, stealing the code from 'sort'.