Use AI_NUMERICSERV if block_dns, and use local getaddrinfo to audit.

This change has two parts:

1. Provide our own local implementation of numeric-only getaddrinfo
   in auditdns.c used to audit for DNS leaks, rather than deferring
   to dlsym(RTLD_NEXT, "getaddrinfo"), in terms of inet_pton.

   To keep review and implementation simple, this is limited to
   AI_NUMERICHOST _and_ AI_NUMERICSERV -- this requires that we
   arrange to pass AI_NUMERICSERV in callers too.

2. Wherever we implement block_dns, set AI_NUMERICSERV in addition to
   AI_NUMERICHOST as needed by the new auditdns.c getaddrinfo.

   (In principle this might also avoid other network leaks -- POSIX
   guarantees no name resolution service will be invoked, and gives
   NIS+ as an example.)

   One tiny semantic change to avoid tripping over the auditor:
   kadmin(8) now uses the string "749" rather than the string
   "kerberos-adm".  (Currently we don't audit kadmin(8) for DNS leaks
   but let's avoid leaving a rake to step on.)  Every other caller I
   found is already guaranteed to pass a numeric service rather than
   named service to getaddrinfo.

fix https://github.com/heimdal/heimdal/issues/1212

lib/roken/test-mini_inetd.c

@@ -49,7 +49,7 @@ get_address(int flags, struct addrinfo ** ret)
 
     memset(&ai, 0, sizeof(ai));
 
-    ai.ai_flags = flags | AI_NUMERICHOST;
+    ai.ai_flags = flags | AI_NUMERICHOST | AI_NUMERICSERV;
     ai.ai_family = AF_INET;
     ai.ai_socktype = SOCK_STREAM;
     ai.ai_protocol = PF_UNSPEC;