include problem PairData in error message

Users occasionally report this error firing, and I can't see why,
so include the rejected PairData in the error message.

This is safe even if it contains evil escape characters, because showing
it displays them in escaped form.

This commit was sponsored by Bruno BEAUFILS on Patreon.

Assistant/Threads/PairListener.hs

@@ -49,8 +49,8 @@ pairListenerThread urlrenderer = namedThread "PairListener" $ do
 					debug ["ignoring message that looped back"]
 					go reqs cache sock
 				(_, _, False, _) -> do
-					liftAnnex $ warning
-						"illegal control characters in pairing message; ignoring"
+					liftAnnex $ warning $
+						"illegal control characters in pairing message; ignoring (" ++ show (pairMsgData m) ++ ")"
 					go reqs cache sock
 				-- PairReq starts a pairing process, so a
 				-- new one is always heeded, even if