[Users] Display only radio buttons (not check boxes) with multiple overlay groups

[Lela Prashad]

I want to use GeoExt to have one base layer group (with multiple base
layers)  using the gx_baselayercontainer node type and two other
overlay groups  (each group with multiple layers) with async node
type. I want to use radio buttons so that only one layer per overlay
group shows up at any time.

I used the TreeNodes example to create my two overlay groups
(http://dev.geoext.org/trunk/geoext/examples/tree.html) and right now
they are working with checkboxes - but I want radio buttons instead.

I tried to follow this GeoExt post on setting up radio buttons for
subnode but found that Andreas said that the Treenodes example code
segment
OpenLayers.Format.JSON().write
was not meant for "real-life application":
http://www.geoext.org/pipermail/users/2009-October/000270.html