Fix backward compatibility issue

Grails is using the method

Author: daniellansun

src/main/java/org/codehaus/groovy/classgen/VariableScopeVisitor.java

@@ -346,6 +346,13 @@ private void checkVariableContextAccess(final Variable variable, final Expressio
     }
 
     //--------------------------------------------------------------------------
+    /**
+     * Sets the current class node context.
+     */
+    public void prepareVisit(ClassNode node) {
+        currentClass = node;
+        currentScope.setClassScope(node);
+    }
 
     @Override
     public void visitClass(final ClassNode node) {