Add cstring import to examples using memset (#289)

* Add cstring import to examples using memset

* Add cstring to deferred tests

Author: etr

examples/deferred_with_accumulator.cpp

@@ -19,6 +19,7 @@
 */
 
 #include <atomic>
+#include <cstring>
 // cpplint errors on chrono and thread because they are replaced (in Chromium) by other google libraries.
 // This is not an issue here.
 #include <chrono> // NOLINT [build/c++11]

examples/minimal_deferred.cpp

@@ -18,6 +18,7 @@
      USA
 */
 
+#include <cstring>
 #include <httpserver.hpp>
 
 static int counter = 0;

test/integ/deferred.cpp

@@ -30,6 +30,7 @@
 #include <sys/socket.h>
 #endif
 
+#include <cstring>
 #include <curl/curl.h>
 #include <signal.h>
 #include <unistd.h>