* tools/gpgtar-create.c (global_header_count): new.
(myreadlink): New.
(build_header): New arg r_exthdr.  Detect and store long file and link
names.  Factor checkum computation out to ...
(compute_checksum): new.
(add_extended_header_record): New.
(write_extended_header): New.
(write_file): Write extended header.