Functionality to specify repeat commands i.e. if a keybinding is used twice, it is possible to use another callback or overrideId for the subsequent times the keybinding is used.
Using the ISEARCH_FORWARD_AGAIN as a context sensitive command and not as a repeatable command. This change is required if we want to add the ISEARCH_BACKWARD to the list that is prefixed by Ctrl-S.
Making the ISEARCH_BACKWARD command work. However there is a problem with registering the context sensitive commands. For registering these commands, another strategy needs to be devised.