(password access) specify comment field in generated ssh pub key

since gl-shell-setup runs as root, the comment in the generated key was
'root@...' instead of whatever userid it was being created for.

This does not affect gitolite or ssh but it seems some people don't
treat "comment" and "comment" and actually *do* stuff with it.

(only code is from author; commit message is from committer)

contrib/real-users/gl-shell-setup

@@ -59,7 +59,7 @@ then
     }
 
     [ -f .ssh/id_rsa.pub ] || {
-        ssh-keygen -q -N "" -f .ssh/id_rsa >&2
+        ssh-keygen -q -N "" -C $user@`hostname` -f .ssh/id_rsa >&2
         chown $user .ssh/id_rsa .ssh/id_rsa.pub
         chmod go-rw .ssh/id_rsa
         chmod go-w  .ssh/id_rsa.pub