Accept only position-sensitive (file-selection) options in file list files.

Accept only position-sensitive (file-selection) options in file list files.

Using such options as -f, -z, etc. is senseless in the file list file
and bypasses the option consistency checks in decode_options.  Therefore,
only options related to file selection (a.k.a position-sensitive options)
are allowed in files.

* doc/tar.texi: Document changes.
* src/common.h (tar_args): Move from tar.c
(TAR_ARGS_INITIALIZER): New macro.
* src/names.c: Declare option group identifiers as an enum.
(names_parse_opt): Special handling for ARGP_KEY_ERROR.
(names_argp): Remove static qualifier.
(names_argp_children): Remove.
* src/tar.c: Declare option group identifiers as an enum.
(parse_opt): Special handling for ARGP_KEY_INIT.
(argp_children): New static variable.
(args): Remove static variable.
(more_options): Allow only options from names_argp.
(parse_default_options): Take a pointer to struct tar_args as argument.
Replace the loc member during the call to argp_parse and restore it
afterwards.
(decode_options): Use automatic variable for args.