Cache SRV records.

Inpsired by a patch from Jeremy Allison, but completely re-rolled
by srk. All bugs are mine.

src/auth.c

@@ -129,7 +129,7 @@ size_t answer_auth(struct dns_header *header, char *limit, size_t qlen, time_t n
 
   for (q = ntohs(header->qdcount); q != 0; q--)
     {
-      unsigned short flag = 0;
+      unsigned int flag = 0;
       int found = 0;
       int cname_wildcard = 0;