mini cleanup and improve comment TODO

gtsam_unstable/nonlinear/Expression-inl.h

@@ -733,8 +733,8 @@ public:
   virtual T value(const Values& values) const {
     using boost::none;
     return function_(this->template expression<A1, 1>()->value(values),
-    this->template expression<A2, 2>()->value(values),
-    none, none);
+        this->template expression<A2, 2>()->value(values),
+        none, none);
   }
 
   /// Construct an execution trace for reverse AD

gtsam_unstable/nonlinear/Expression.h

@@ -116,7 +116,7 @@ public:
     return root_->traceSize();
   }
 
-  /// trace execution, very unsafe, for testing purposes only
+  /// trace execution, very unsafe, for testing purposes only //TODO this is not only used for testing, but in value() below!
   T traceExecution(const Values& values, ExecutionTrace<T>& trace,
       char* raw) const {
     return root_->traceExecution(values, trace, raw);