security: Added SecurityException.what.
diff --git a/ndn-cpp/security/security-exception.hpp b/ndn-cpp/security/security-exception.hpp
index 0a3d20c..28d87f5 100644
--- a/ndn-cpp/security/security-exception.hpp
+++ b/ndn-cpp/security/security-exception.hpp
@@ -20,7 +20,9 @@
     
   virtual ~SecurityException() throw();
     
-  inline std::string Msg() { return errorMessage_; }
+  std::string Msg() { return errorMessage_; }
+
+  std::string what() { return errorMessage_; }
     
 private:
   const std::string errorMessage_;