Any two conflicting options are reported only if they both occur in
the command line. Otherwise, options defined in the command line
silently override those set in the TAR_OPTIONS environment variable.
* src/common.h (option_source): New enum.
(option_locus): New struct.
* src/names.c (name_elt): New member: line.
(name_add_file): Initialize line.
(read_name_from_file): Keep track of input line number for diagnostic
purposes.
(handle_option): Take a pointer to struct name_elt as 2nd parameter;
pass locus info to more_options().
* src/tar.c (tar_args): New member: loc.
(option_class): New enum.
(optloc_save,optloc_lookup)
(option_set_in_cl,optloc_eq): New functions.
(set_use_compress_program_option): Take into account option location.
(set_old_files_option): New function.
(parse_opt): Keep track of option locations.
(more_options): Improve error reporting.
(parse_default_options): New function.
(decode_options): Parse TAR_OPTION and command line separately.
Options from the latter silently override those from the former.
* lib/prepargs.c: Remove.
* lib/prepargs.h: Remove.
* lib/Makefile.am: Update.
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