get, move, copy, mirror: Added --failed switch which retries failed copies/moves

Note that get --from foo --failed will get things that a previous get --from bar
tried and failed to get, etc. I considered making --failed only retry
transfers from the same remote, but it was easier, and seems more useful,
to not have the same remote requirement.

Noisy due to some refactoring into Types/

Command/Drop.hs

@@ -41,7 +41,7 @@ optParser desc = DropOptions
 	<$> cmdParams desc
 	<*> optional parseDropFromOption
 	<*> parseAutoOption
-	<*> optional (parseKeyOptions False)
+	<*> optional parseKeyOptions
 	<*> parseBatchOption
 
 parseDropFromOption :: Parser (DeferredParse Remote)