rib: a few cleanups and simplifications in RibManager

Change-Id: I77699525ab372c4f4f3bbcae74e65bec24a86b4c
Refs: #3903
diff --git a/core/manager-base.hpp b/core/manager-base.hpp
index e947b8d..3d0a465 100644
--- a/core/manager-base.hpp
+++ b/core/manager-base.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2014-2016,  Regents of the University of California,
+ * Copyright (c) 2014-2017,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -59,8 +59,10 @@
   };
 
 public:
-  ManagerBase(Dispatcher& dispatcher,
-              const std::string& module);
+  ManagerBase(Dispatcher& dispatcher, const std::string& module);
+
+  virtual
+  ~ManagerBase();
 
   const std::string&
   getModule() const
@@ -69,7 +71,6 @@
   }
 
 PUBLIC_WITH_TESTS_ELSE_PROTECTED: // registrations to the dispatcher
-
   // difference from mgmt::ControlCommand: accepts nfd::ControlParameters
   typedef function<void(const ControlCommand& command,
                         const Name& prefix, const Interest& interest,