Add temporary exception for unsupported (as of yet) combo of delegating creator, external type id

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/deser/BeanDeserializer.java

@@ -716,6 +716,10 @@ protected Object deserializeWithExternalTypeId(JsonParser p, DeserializationCont
         if (_propertyBasedCreator != null) {
             return deserializeUsingPropertyBasedWithExternalTypeId(p, ctxt);
         }
+        if (_delegateDeserializer != null) {
+            return deserializeUsingDelegateWithExternalTypeId(p, ctxt);
+        }
+
         return deserializeWithExternalTypeId(p, ctxt, _valueInstantiator.createUsingDefault(ctxt));
     }
 
@@ -856,4 +860,13 @@ protected Object deserializeUsingPropertyBasedWithExternalTypeId(JsonParser p, D
             return null; // never gets here
         }
     }
+
+    /**
+     * @since 2.7
+     */
+    protected Object deserializeUsingDelegateWithExternalTypeId(JsonParser p, DeserializationContext ctxt)
+        throws IOException
+    {
+        throw ctxt.mappingException("Combination of External Type Id, Delegating Creator not yet supported");
+    }
 }