reset attributed variable state between toplevel queries (#242)

src/prolog/machine/attributed_variables.rs

@@ -32,9 +32,9 @@ impl AttrVarInitializer {
 
     #[inline]
     pub(super) fn reset(&mut self) {
+	self.attribute_goals.clear();
         self.attr_var_queue.clear();
         self.bindings.clear();
-	self.attribute_goals.clear();
     }
 }
 

src/prolog/machine/system_calls.rs

@@ -1680,6 +1680,9 @@ impl MachineState {
                     }
                 };
             },
+            &SystemClauseType::ResetAttrVarState => {
+                self.attr_var_init.reset();
+            }
             &SystemClauseType::RemoveCallPolicyCheck => {
                 let restore_default = match call_policy.downcast_mut::<CWILCallPolicy>().ok() {
                     Some(call_policy) => {