Made abstract_objectt::type() virtual

context_abstract_objectt:type() wanted to override it, but because the
base class method wasn't virtual was just hiding it.

Author: jezhiggins

src/analyses/variable-sensitivity/abstract_object.h

@@ -121,7 +121,7 @@ class abstract_objectt : public std::enable_shared_from_this<abstract_objectt>
   /// Get the real type of the variable this abstract object is representing.
   ///
   /// \return The program type this abstract object represents
-  const typet &type() const;
+  virtual const typet &type() const;
 
   /// Find out if the abstract object is top
   ///

src/analyses/variable-sensitivity/context_abstract_object.h

@@ -55,7 +55,7 @@ class context_abstract_objectt : public abstract_objectt
   {
   }
 
-  virtual const typet &type() const
+  const typet &type() const override
   {
     return child_abstract_object->type();
   }