Added comment

gtsam/base/debug.h

@@ -44,7 +44,7 @@
 namespace gtsam {
   GTSAM_EXTERN_EXPORT FastMap<std::string, ValueWithDefault<bool,false> > debugFlags;
 
-  // thread-safe functions to access debugFlags map
+  // Non-guarded use led to crashes, and solved in commit cd35db2
   bool GTSAM_EXPORT guardedIsDebug(const std::string& s);
   void GTSAM_EXPORT guardedSetDebug(const std::string& s, const bool v);
 }