Work correctly if your nameserver is ::1

We had all the code in place to handle this right... except that we
were unconditionally opening a PF_INET socket instead of looking at
sa_family.  Ow.

Fixes bug 2574; not a bugfix on any particular version, since this
never worked before.

changes/bug2574

@@ -0,0 +1,2 @@
+  o Minor features:
+    - Allow nameserves with IPv6 address. Fixes bug 2574.

src/or/eventdns.c

@@ -2320,7 +2320,7 @@ _evdns_nameserver_add_impl(const struct sockaddr *address,
 	memset(ns, 0, sizeof(struct nameserver));
 	ns->timeout_event_deleted = __LINE__;
 
-	ns->socket = socket(PF_INET, SOCK_DGRAM, 0);
+	ns->socket = socket(address->sa_family, SOCK_DGRAM, 0);
 	if (ns->socket < 0) { err = 1; goto out1; }
 #ifdef WIN32
 	{