[chord] Some new vis features

[Emil Sit]

In case you are not on chord-cvs...

> New features!
> * In geo mode, switch between viewing xy (default), yz, and xz
>   coordinates by pressing '1', '2', '3' respectively.

I'd like eventually to improve this (incrementally) by rotating (90
degrees) about the current center.  right now, you must recenter
after switching modes.  it might also be nice if we displayed the
'x' and 'y' ranges on the sides of the window somewhere, to get a
feel for where in the space we are located.

of course, one day, full 3d projection would be cool :-)

> * In geo mode, right click to center view at where you clicked.
> * In geo mode, press 'z' to zoom out and 'Z' to zoom in.  Use with
>   right clicking for zooming fun. 

The current zoom factor is 1.2, which seems okay for interactive use.

> * After selecting nodes with the middle button, press 'g' to
>   force vis to try to update those nodes immediately.

The other caveat about this update is that there are no new
buttons.  It wouldn't be too terribly difficult to add zoom-in,
zoom-out, and update-selected buttons.