handler_ptr gives the strong exception guarantee (API Change):

* The handler_ptr constructor now provides the
  strong exception guarantee.

* The signature for managed objects constructed by
  `handler_ptr` receives a const reference to the handler.

Actions required:

* Change the constructor signature for state objects
  used with handler_ptr to receive a const reference to
  the handler.

test/beast/core/handler_ptr.cpp

@@ -34,7 +34,8 @@ public:
 
     struct T
     {
-        T(handler&)
+        explicit
+        T(handler const&)
         {
         }
 
@@ -45,7 +46,8 @@ public:
 
     struct U
     {
-        U(handler&)
+        explicit
+        U(handler const&)
         {
             throw std::exception{};
         }