Returns the value (as a string) of the specified property.
The arguments are:
property: The property atom, as an example GDK.Atom.__SWM_VROOT
offset (optional): The starting offset, in elements
delete_when_done (optional): If set, the property will be deleted when it has
been fetched.
Example usage: Find the 'virtual' root window (many window managers
put large windows over the screen)
GDK.Window root = GTK.root_window();
array maybe=root->children()->
get_property(GDK.Atom.__SWM_VROOT)-({0});
if(sizeof(maybe))
root=GDK.Window( maybe[0]->data[0] );