Further patching for GAE compatibility.

Since net.ListenTCP, net.ListenUDP and net.TCPListener are not defined
in the GAE standard library these build flags will stop those files from
being imported.  A better solution would have been to break up this
monolithic package into smaller parts.

server.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !appengine
+
 // DNS server implementation.
 
 package dns

server_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !appengine
+
 package dns
 
 import (