more time stopping functionality

Author: Daniel Kroening

src/util/time_stopping.h

@@ -72,6 +72,8 @@ class time_periodt:public fine_timet
   {
     return time_periodt(t-other.t);
   }
+
+  friend class absolute_timet;
 };
 
 class absolute_timet:public fine_timet
@@ -89,6 +91,16 @@ class absolute_timet:public fine_timet
   {
     return time_periodt(t-other.t);
   }
+
+  absolute_timet operator+(const time_periodt &other)
+  {
+    return absolute_timet(t+other.t);
+  }
+
+  bool operator>=(const absolute_timet &other)
+  {
+    return t>=other.t;
+  }
 };
 
 absolute_timet current_time();