Enable drag and drop for treeview?

[Jef Driesen <jefdriesen hotmail com>]

For my application, I want to be able to re-order rows in a treeview 
(treestore model) using drag and drop. According to the gtkmm book, I 
can use set_reorderable(). But how can I detect when a drag and drop 
operation is finished (to update the underlying database)? I can't find 
any signals to connect to. Am I missing something?