Converting a Glib::ValueBase to a derived type

[José Alburquerque <jaalburquerque cox net>]

I'm wondering, would anyone know how to convert a Glib::ValueBase to one 
of its derived types (such as Glib::Value<int>) assuming the derived 
type has been returned from a function as the base class 
Glib::ValueBase?  I'm writing some code that would conveniently return a 
derived Glib::ValueBase as a Glib::ValueBase and really don't know how 
to convert it back to the derived type once it's been returned.  Thanks.

-Jose