Merge branch 'jk/big-and-future-archive-tar'

"git archive" learned to handle files that are larger than 8GB and commits far in the future than expressible by the traditional US-TAR format. * jk/big-and-future-archive-tar: archive-tar: drop return value archive-tar: write extended headers for far-future mtime archive-tar: write extended headers for file sizes >= 8GB t5000: test tar files that overflow ustar headers t9300: factor out portable "head -c" replacement