Variant

- Salvaged Variant code from older project, for use in expression
  evaluation.

src/Duration.h

@@ -42,8 +42,8 @@ public:
   Duration& operator= (const Duration&);
   ~Duration ();                          // Destructor
 
-  operator time_t ();
-  operator std::string ();
+  operator time_t () const;
+  operator std::string () const;
 
   std::string format () const;
   std::string formatCompact () const;