completion: offer '--edit-todo' during interactive rebase

Helped-by: John Keeping <john@keeping.me.uk>
Helped-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: t-b

contrib/completion/git-completion.bash

@@ -1667,7 +1667,10 @@ _git_push ()
 _git_rebase ()
 {
 	local dir="$(__gitdir)"
-	if [ -d "$dir"/rebase-apply ] || [ -d "$dir"/rebase-merge ]; then
+	if [ -f "$dir"/rebase-merge/interactive ]; then
+		__gitcomp "--continue --skip --abort --edit-todo"
+		return
+	elif [ -d "$dir"/rebase-apply ] || [ -d "$dir"/rebase-merge ]; then
 		__gitcomp "--continue --skip --abort"
 		return
 	fi