With the --prune (or -p) option, git remote update will also prune
all the remotes that it fetches. Previously, you had to do a manual
git remote prune <remote> for each of the remotes you wanted to
prune, and this could be tedious with many remotes.
A single command will now update a set of remotes, and remove all
stale branches: git remote update -p [group]
Signed-off-by: Finn Arne Gangstad <finnag@pvv.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>