Allow n/p to be repeated while holding down ctrl

...and tapping n or p

Instead of having to tap an an an or ap ap ap while holding control, you
just do ctrl-a (in my case) and then hold control and tap n n n or p p p

Also, I think my code below will work, but the actual bindings I have are:

```
# Quick pane selection
bind -r C-p select-window -t :-
bind -r C-n select-window -t :+
```