Close child process stdin on SIGCHLD

lib/child_process.js

@@ -56,6 +56,7 @@ function ChildProcess () {
   internal.onexit = function (code) {
     gotCHLD = true;
     exitCode = code;
+    stdin.close();
     if (!stdout.readable && !stderr.readable) {
       self.emit('exit', exitCode);
     }