drag autoscroll in a clist (v1.2)

[Patrick Crosby <pcrosby pobox com>]

in gtk1.2.x, i have an application with two clists.  while i'm
dragging a row of a clist, i'd like the clist to scroll vertically
automatically when i drag above or below the clist's window, when
dragging something within the same window or dragging it to the other
clist. 

i've looked at the clist source and it looks like it should happen
without me having to do anything.  it works if the reordering is
enabled on the clist (but just for reordering).

is there some flag that needs to be set?  does it have something to do
with the way i've set up my drag-and-drop?  i've scoured the
documentation and the web to no avail.  everything works fine except
for this... 

thanks.