encourage rejected relays to contact us

When the directory authorities refuse a bad relay's descriptor,
encourage the relay operator to contact us. Many relay operators
won't notice this line in their logs, but it's a win if even a
few learn why we don't like what their relay was doing.

Resolves ticket 18760.

I didn't specify a contact mechanism (e.g. an email address), because
every time we've done that in the past, a few years later we noticed
that the code was pointing people to an obsolete contact address.

changes/feature18760

@@ -0,0 +1,6 @@
+  o Minor features:
+    - When the directory authorities refuse a bad relay's descriptor,
+      encourage the relay operator to contact us. Many relay operators
+      won't notice this line in their logs, but it's a win if even a
+      few learn why we don't like what their relay was doing. Resolves
+      ticket 18760.

src/or/dirserv.c

@@ -349,7 +349,7 @@ dirserv_get_status_impl(const char *id_digest, const char *nickname,
 
   if (result & FP_REJECT) {
     if (msg)
-      *msg = "Fingerprint is marked rejected";
+      *msg = "Fingerprint is marked rejected -- please contact us?";
     return FP_REJECT;
   } else if (result & FP_INVALID) {
     if (msg)
@@ -367,7 +367,7 @@ dirserv_get_status_impl(const char *id_digest, const char *nickname,
     log_fn(severity, LD_DIRSERV, "Rejecting '%s' because of address '%s'",
                nickname, fmt_addr32(addr));
     if (msg)
-      *msg = "Authdir is rejecting routers in this range.";
+      *msg = "Suspicious relay address range -- please contact us?";
     return FP_REJECT;
   }
   if (!authdir_policy_valid_address(addr, or_port)) {