keep track of the stage we're at in pairing

This avoids us responding to our own pairing messages, as well
as ignoring any out of order messages that might be received somehow.

Assistant/Pairing.hs

@@ -26,7 +26,7 @@ data PairStage
 	| PairAck
 	{- "I saw your PairAck; you can stop sending them." -}
 	| PairDone
-	deriving (Eq, Read, Show)
+	deriving (Eq, Read, Show, Ord)
 
 newtype PairMsg = PairMsg (Verifiable (PairStage, PairData, SomeAddr))
 	deriving (Eq, Read, Show)
@@ -66,6 +66,7 @@ data PairingInProgress = PairingInProgress
 	, inProgressThreadId :: Maybe ThreadId
 	, inProgressSshKeyPair :: SshKeyPair
 	, inProgressPairData :: PairData
+	, inProgressPairStage :: PairStage
 	}
 
 data SomeAddr = IPv4Addr HostAddress | IPv6Addr HostAddress6