One more event::signal() member to put back.

asio/include/asio/detail/std_event.hpp

diff --git a/asio/include/asio/detail/std_event.hpp b/asio/include/asio/detail/std_event.hpp
index 29af66c..027e10d 100644
--- a/asio/include/asio/detail/std_event.hpp
+++ b/asio/include/asio/detail/std_event.hpp
@@ -44,6 +44,13 @@
   {
   }
 
+  // Signal the event. (Retained for backward compatibility.)
+  template <typename Lock>
+  void signal(Lock& lock)
+  {
+    this->signal_all(lock);
+  }
+
   // Signal all waiters.
   template <typename Lock>
   void signal_all(Lock& lock)