gitk: Make vi-style keybindings more vi-like

gitk: Make vi-style keybindings more vi-like

When commit 6e2dda35 (Add new keybindings, 2005-09-22) added vi-style
keybindings to gitk (an excellent idea!), instead of adopting the
usual "hjkl = left, down, up, right" bindings used by less, vi, rogue,
and many other programs, it used "ijkl = up, left, down, right" to
mimic the inverted-T formation of the arrow keys on a qwerty keyboard,
in the style of Lode runner.  So using 'j' and 'k' to scroll through
commits produces utterly confusing results to the vi user, as 'k'
moves down and 'j' moves to the previous commit.

Luckily most non-vi-users are probably using an alternate set of keys
(cursor keys or z/x + n/p) anyway.  Switch to the expected vi/nethack
convention.

Requested-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>