Merge branch 'rs/tar-tree' into next

Merge branch 'rs/tar-tree' into next

* rs/tar-tree:
  tar-tree: Use the prefix field of a tar header
  tar-tree: Remove obsolete code
  tar-tree: Use write_entry() to write the archive contents
  tar-tree: Introduce write_entry()
  tar-tree: Use SHA1 of root tree for the basedir
  git-apply: safety fixes
  Removed bogus "<snap>" identifier.
  Clarify and expand some hook documentation.
  commit-tree: check return value from write_sha1_file()
  send-email: Identify author at the top when sending e-mail
  Format tweaks for asciidoc.