avoid unused variable warnings

[[Imported from SVN: r5227]]

common/test/sllisttest.cc

@@ -397,10 +397,12 @@ int main()
 
   double& d = lbegin.dereference();
 
-  d= 2.0;
+  d=2.0;
 
   double& d1 = lbegin.dereference();
 
+  d1=3.0;
+
   lbegin.dereference()=5.0;
 
   lbegin.operator*()=5.0;