Use new signal_set to shut down.

[SVN r71707]

example/http/server/server.cpp

@@ -57,13 +57,6 @@ void server::run()
   io_service_.run();
 }
 
-void server::stop()
-{
-  // Post a call to the stop function so that server::stop() is safe to call
-  // from any thread.
-  io_service_.post(boost::bind(&server::handle_stop, this));
-}
-
 void server::handle_accept(const boost::system::error_code& e)
 {
   if (!e)