don't send PREPARE before INITREMOTE

That complicated special remote programs, because they had to avoid making
PREPARE fail if some configuration is missing, because the remote might not
be initialized yet. Instead, complicate git-annex slightly by only sending
PREPARE immediately before some other request other than INITREMOTE (or
PREPARE of course).

Remote/External/Types.hs

@@ -18,6 +18,7 @@ module Remote.External.Types (
 	Sendable(..),
 	Receivable(..),
 	Request(..),
+	needsPREPARE,
 	Response(..),
 	RemoteRequest(..),
 	RemoteResponse(..),
@@ -60,6 +61,7 @@ data ExternalState = ExternalState
 	{ externalSend :: Handle
 	, externalReceive :: Handle
 	, externalPid :: ProcessHandle
+	, externalPrepared :: Bool
 	}
 
 -- Constructor is not exported, and only created by newExternal.
@@ -98,6 +100,12 @@ data Request
 	| REMOVE Key
 	deriving (Show)
 
+-- Does PREPARE need to have been sent before this request?
+needsPREPARE :: Request -> Bool
+needsPREPARE PREPARE = False
+needsPREPARE INITREMOTE = False
+needsPREPARE _ = True
+
 instance Sendable Request where
 	formatMessage PREPARE = ["PREPARE"]
 	formatMessage INITREMOTE = ["INITREMOTE"]