After Ctrl+O combination in insert or replace mode enter command mode
and after a single command (can consist of entering Ex command or can be
switch to other buffer) or escape key return to previous insert or
replace mode. One exception is that if entering insert mode is part of
the command after <C-O> pressing escape key will exit to command mode
(Vim behavior).

Change-Id: I37d684b691157001e2cab156687d6771afdec7b9
Reviewed-by: hjk <qthjk@ovi.com>