Merge branch 'jt/fetch-pack-error-reporting'

"git fetch-pack" was not prepared to accept ERR packet that the upload-pack can send with a human-readable error message. It showed the packet contents with ERR prefix, so there was no data loss, but it was redundant to say "ERR" in an error message. * jt/fetch-pack-error-reporting: fetch-pack: show clearer error message upon ERR