Improve the keypin failure message

Closes the human-factors part of ticket 22348.

changes/ticket22348

@@ -0,0 +1,5 @@
+  o Minor features (directory authority):
+    - Improve the message that authorities report to relays when
+      the RSA/Ed25519 key pair they present conflicts with a previously
+      pinned key. Closes ticket 22348.
+

src/or/dirserv.c

@@ -720,7 +720,10 @@ dirserv_add_descriptor(routerinfo_t *ri, const char **msg, const char *source)
     log_info(LD_DIRSERV, "Dropping descriptor from %s (source: %s) because "
              "its key did not match an older RSA/Ed25519 keypair",
              router_describe(ri), source);
-    *msg = "Looks like your keypair does not match its older value.";
+    *msg = "Looks like your keypair has changed? This authority previously "
+      "recorded a different RSA identity for this Ed25519 identity (or vice "
+      "versa.) Did you replace or copy some of your key files, but not "
+      "the others?";
     r = ROUTER_AUTHDIR_REJECTS;
     goto fail;
   }