Merge branch 'jk/peel-ref'

Speeds up "git upload-pack" (what is invoked by "git fetch" on the other side of the connection) by reducing the cost to advertise the branches and tags that are available in the repository. * jk/peel-ref: upload-pack: use peel_ref for ref advertisements peel_ref: check object type before loading peel_ref: do not return a null sha1 peel_ref: use faster deref_tag_noverify