Bugfix history navigation after adding duplicate lines

[tlk]

This fixes a small bug caused by the history index not always being reset.

So a user could go through a session like this:

> 1    # user typed 1, then enter
> 2    # user typed 2, then enter
> 2    # user pressed key-up, then enter
> 1    # user pressed key-up again and expected 2 but this time the history index was off

[andybest]

Awesome, thanks :)

[tlk]

Thank you very much!