implement remove-before

The reason to use removeBeforeRemoteEndTime is twofold.

First, removeBefore sends two protocol commands. Currently, the HTTP
protocol runner only supports sending a single command per invocation.

Secondly, the http server gets a monotonic timestamp from the client. So
translating back to a POSIXTime would be annoying.

The timestamp flow with a proxy will be:

- client gets timestamp, which gets the monotonic timestamp from the
  proxied remote via the proxy. The timestamp is currently not
  proxied when there is a single proxy.
- client calls remove-before
- http server calls removeBeforeRemoteEndTime which sends REMOVE-BEFORE
  to the proxied remote.

P2P/Protocol.hs

@@ -437,15 +437,18 @@ removeBefore endtime key = do
 			let remoteendtime = remotetime + timeleft'
 			if timeleft <= 0
 				then return (Right False, Nothing)
-				else do
-					net $ sendMessage $
-						REMOVE_BEFORE remoteendtime key
-					checkSuccessFailurePlus	
+				else removeBeforeRemoteEndTime remoteendtime key
 		Just (ERROR err) -> return (Left err, Nothing)
 		_ -> do
 			net $ sendMessage (ERROR "expected TIMESTAMP")
 			return (Right False, Nothing)
 
+removeBeforeRemoteEndTime :: MonotonicTimestamp -> Key -> Proto (Either String Bool, Maybe [UUID])
+removeBeforeRemoteEndTime remoteendtime key = do
+	net $ sendMessage $
+		REMOVE_BEFORE remoteendtime key
+	checkSuccessFailurePlus	
+
 get :: FilePath -> Key -> Maybe IncrementalVerifier -> AssociatedFile -> Meter -> MeterUpdate -> Proto (Bool, Verification)
 get dest key iv af m p = 
 	receiveContent (Just m) p sizer storer $ \offset ->