extension completions stay for too long

[cjhopman]

if you type some_list.app then we will suggest completing to append(object). That's good. But when you keep typing and type out "some_list.append(obj" we still have that suggested completion and then when you type "some_list.append(obj)" the suggestion is still there, and then when you hit enter you accept the suggestion and we replace your code with "some_list.append". This is bad.