Clicking on a GtkCellRendererPixbuf

[Calum Grant <calumg onetel com>]

I have a GtkTreeView, which contains several GtkCellRendererToggle 
columns.  I'd like to replace them with a GtkCellRendererPixbuf column, 
with three possible states.

I can change the pixbuf in the column no problems.  But I'd like the 
column to respond to mouse clicks, like a GtkCellRendererToggle.  How do 
I intercept mouse clicks to this column?

Calum Grant