Merge branch 'jc/boundary'

Merge branch 'jc/boundary'

* jc/boundary:
  git-bundle: prevent overwriting existing bundles
  git-bundle: die if a given ref is not included in bundle
  git-bundle: handle thin packs in subcommand "unbundle"
  git-bundle: Make thin packs
  git-bundle: avoid packing objects which are in the prerequisites
  bundle: fix wrong check of read_header()'s return value & add tests
  revision --boundary: fix uncounted case.
  revision --boundary: fix stupid typo
  git-bundle: make verify a bit more chatty.
  revision traversal: SHOWN means shown
  git-bundle: various fixups
  revision traversal: retire BOUNDARY_SHOW
  revision walker: Fix --boundary when limited