disallow providing multiple upstream branches to rebase, pull --rebase

It does not make sense to provide multiple upstream branches to either
git pull --rebase, or to git rebase, so disallow both.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-pull.sh

@@ -171,6 +171,11 @@ case "$merge_head" in
 		echo >&2 "Cannot merge multiple branches into empty head"
 		exit 1
 	fi
+	if test true = "$rebase"
+	then
+		echo >&2 "Cannot rebase onto multiple branches"
+		exit 1
+	fi
 	;;
 esac
 

git-rebase.sh

@@ -310,6 +310,7 @@ do
 	esac
 	shift
 done
+test $# -gt 2 && usage
 
 # Make sure we do not have $GIT_DIR/rebase-apply
 if test -z "$do_merge"