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/actions/set_rsc.h

@@ -43,7 +43,7 @@ class SetRSC : public Action {
     bool init(std::string *error) override;
 
  private:
-    std::unique_ptr<RunTimeString> m_string;
+    std::shared_ptr<RunTimeString> m_string;
 };