add VerifiedCopy data type

There should be no behavior changes in this commit, it just adds a more
expressive data type and adjusts code that had been passing around a [UUID]
or sometimes a Maybe Remote to instead use [VerifiedCopy].

Although, since some functions were taking two different [UUID] lists,
there's some potential for me to have gotten it horribly wrong.

Annex/Drop.hs

@@ -32,9 +32,8 @@ type Reason = String
  - only ones that match the UUIDs will be dropped from.
  - If allowed to drop fromhere, that drop will be tried first.
  -
- - A remote can be specified that is known to have the key. This can be
- - used an an optimisation when eg, a key has just been uploaded to a
- - remote.
+ - A VerifiedCopy can be provided as an optimisation when eg, a key
+ - has just been uploaded to a remote.
  -
  - In direct mode, all associated files are checked, and only if all
  - of them are unwanted are they dropped.
@@ -42,8 +41,8 @@ type Reason = String
  - The runner is used to run commands, and so can be either callCommand
  - or commandAction.
  -}
-handleDropsFrom :: [UUID] -> [Remote] -> Reason -> Bool -> Key -> AssociatedFile -> Maybe Remote -> (CommandStart -> CommandCleanup) -> Annex ()
-handleDropsFrom locs rs reason fromhere key afile knownpresentremote runner = do
+handleDropsFrom :: [UUID] -> [Remote] -> Reason -> Bool -> Key -> AssociatedFile -> [VerifiedCopy] -> (CommandStart -> CommandCleanup) -> Annex ()
+handleDropsFrom locs rs reason fromhere key afile preverified runner = do
 	fs <- ifM isDirect
 		( do
 			l <- associatedFilesRelative key
@@ -112,7 +111,7 @@ handleDropsFrom locs rs reason fromhere key afile knownpresentremote runner = do
 			)
 
 	dropl fs n = checkdrop fs n Nothing $ \numcopies ->
-		Command.Drop.startLocal afile numcopies key knownpresentremote
+		Command.Drop.startLocal afile numcopies key preverified
 
 	dropr fs r n  = checkdrop fs n (Just $ Remote.uuid r) $ \numcopies ->
 		Command.Drop.startRemote afile numcopies key r