Merge branch 'nd/upload-pack-shallow'

Serving objects from a shallow repository needs to write a temporary file to be used, but the serving upload-pack may not have write access to the repository which is meant to be read-only. Instead feed these temporary shallow bounds from the standard input of pack-objects so that we do not have to use a temporary file. * nd/upload-pack-shallow: upload-pack: send shallow info over stdin to pack-objects