Adds new method for rule merge

IMPORTANT: SecDefaultAction specified on a child configuration will
overwrite the ones specified on the parent; Previously it was
concatenating.

src/operators/detect_xss.h

@@ -33,7 +33,7 @@ class DetectXSS : public Operator {
 
     bool evaluate(Transaction *t, RuleWithActions *rule,
         const std::string& input,
-        std::shared_ptr<RuleMessage> ruleMessage) override;
+        RuleMessage *ruleMessage) override;
 };
 
 }  // namespace operators