hook close() to prevent rude programs like ssh to close our pipes

those pipes are needed to talk with the dns-name allocator thread.

closes #9

src/allocator_thread.h

@@ -6,6 +6,9 @@
 
 #define MSG_LEN_MAX 256
 
+extern int req_pipefd[2];
+extern int resp_pipefd[2];
+
 void at_init(void);
 void at_close(void);
 size_t at_get_host_for_ip(ip_type ip, char* readbuf);