Merge pull request #477 from vstakhov/master

Add -n option to pkg-check.
Turn pkg_emit_manifest into a stub that calls pkg_emit_manuifest2

pkg_emit_manifest2 takes an allocated struct sbuf, and reuse it.
Manifest can now emit et load path, pkg size and sum of packages
pkg repo now generates repository in yaml formats.

packagesite.txz is the new repository in yaml formats it contains a
packagesite.yaml file and it can be signed.