mapper: Correct GetInterfaceType(Type,string)
mapper: Correct GetInterfaceType(Type,string)

In recent commits I had neglected to consider that some users of
dbus-sharp will be subclassing MarshalByRefObject.

This commit corrects that, adding a simple GetHierarchy function to
return the type and its ancestors.

arfbtwn/dbus-sharp,arfbtwn/dbus-sharp