drop unwanted content in the transfer scan

This was complicated quite a bit by needing to check numcopies. I optimised
that, so it only looks up numcopies once per file, no matter how many
remotes it checks to drop from. Although it did just occur to me that
it might be better to first check if it wants to drop content, and only
then check numcopies..

Command/Drop.hs

@@ -48,7 +48,7 @@ startLocal file numcopies key = stopUnless (inAnnex key) $ do
 
 startRemote :: FilePath -> Maybe Int -> Key -> Remote -> CommandStart
 startRemote file numcopies key remote = do
-	showStart "drop" file
+	showStart ("drop " ++ Remote.name remote) file
 	next $ performRemote key numcopies remote
 
 performLocal :: Key -> Maybe Int -> CommandPerform