toward SafeDropProof expiry checking

Added Maybe POSIXTime to SafeDropProof, which gets set when the proof is
based on a LockedCopy. If there are several LockedCopies, it uses the
closest expiry time. That is not optimal, it may be that the proof
expires based on one LockedCopy but another one has not expired. But
that seems unlikely to really happen, and anyway the user can just
re-run a drop if it fails due to expiry.

Pass the SafeDropProof to removeKey, which is responsible for checking
it for expiry in situations where that could be a problem. Which really
only means in Remote.Git.

Made Remote.Git check expiry when dropping from a local remote.

Checking expiry when dropping from a P2P remote is not yet implemented.
P2P.Protocol.remove has SafeDropProof plumbed through to it for that
purpose.

Fixing the remaining 2 build warnings should complete this work.

Note that the use of a POSIXTime here means that if the clock gets set
forward while git-annex is in the middle of a drop, it may say that
dropping took too long. That seems ok. Less ok is that if the clock gets
turned back a sufficient amount (eg 5 minutes), proof expiry won't be
noticed. It might be better to use the Monotonic clock, but that doesn't
advance when a laptop is suspended, and while there is the linux
Boottime clock, that is not available on other systems. Perhaps a
combination of POSIXTime and the Monotonic clock could detect laptop
suspension and also detect clock being turned back?

There is a potential future flag day where
p2pDefaultLockContentRetentionDuration is not assumed, but is probed
using the P2P protocol, and peers that don't support it can no longer
produce a LockedCopy. Until that happens, when git-annex is
communicating with older peers there is a risk of data loss when
a ssh connection closes during LOCKCONTENT.

Command/Drop.hs

@@ -151,7 +151,7 @@ performRemote pcc key afile numcopies mincopies remote ud = do
 				, "proof:"
 				, show proof
 				]
-			ok <- Remote.action (Remote.removeKey remote key)
+			ok <- Remote.action (Remote.removeKey remote proof key)
 			next $ cleanupRemote key remote ud ok
 		, stop
 		)

Command/Fsck.hs

@@ -639,7 +639,7 @@ badContentRemote remote localcopy key = do
 					)
 		)
 
-	dropped <- tryNonAsync (Remote.removeKey remote key)
+	dropped <- tryNonAsync (Remote.removeKey remote Nothing key)
 	when (isRight dropped) $
 		Remote.logStatus remote key InfoMissing
 	return $ case (movedbad, dropped) of

Command/Move.hs

@@ -296,23 +296,26 @@ fromPerform' present updatelocationlog src key afile = do
 fromDrop :: Remote -> UUID -> DestStartedWithCopy -> Key -> AssociatedFile -> ([UnVerifiedCopy] -> [UnVerifiedCopy])-> CommandPerform
 fromDrop src destuuid deststartedwithcopy key afile adjusttocheck =
 	willDropMakeItWorse (Remote.uuid src) destuuid deststartedwithcopy key afile >>= \case
-		DropAllowed -> dropremote "moved"
+		DropAllowed -> dropremote Nothing "moved"
 		DropCheckNumCopies -> do
 			(numcopies, mincopies) <- getSafestNumMinCopies afile key
 			(tocheck, verified) <- verifiableCopies key [Remote.uuid src]
 			verifyEnoughCopiesToDrop "" key (Just (Remote.uuid src)) Nothing numcopies mincopies [Remote.uuid src] verified
-				(adjusttocheck tocheck) (dropremote . showproof) faileddropremote
+				(adjusttocheck tocheck) dropremotewithproof faileddropremote
 		DropWorse -> faileddropremote
   where
 	showproof proof = "proof: " ++ show proof
 
-	dropremote reason = do
+	dropremotewithproof proof = 
+		dropremote (Just proof) (showproof proof)
+
+	dropremote mproof reason = do
 		fastDebug "Command.Move" $ unwords
 			[ "Dropping from remote"
 			, show src
 			, "(" ++ reason ++ ")"
 			]
-		ok <- Remote.action (Remote.removeKey src key)
+		ok <- Remote.action (Remote.removeKey src mproof key)
 		when ok $
 			logMoveCleanup deststartedwithcopy
 		next $ Command.Drop.cleanupRemote key src (Command.Drop.DroppingUnused False) ok

Command/TestRemote.hs

@@ -303,7 +303,7 @@ test runannex mkr mkk =
 			Right v -> return (True, v)
 			Left _ -> return (False, UnVerified)
 	store r k = Remote.storeKey r k (AssociatedFile Nothing) Nothing nullMeterUpdate
-	remove r k = Remote.removeKey r k
+	remove r k = Remote.removeKey r Nothing k
 
 testExportTree :: RunAnnex -> Annex (Maybe Remote) -> Annex Key -> Annex Key -> [TestTree]
 testExportTree runannex mkr mkk1 mkk2 =
@@ -366,7 +366,7 @@ testExportTree runannex mkr mkk1 mkk2 =
 testUnavailable :: RunAnnex -> Annex (Maybe Remote) -> Annex Key -> [TestTree]
 testUnavailable runannex mkr mkk =
 	[ check isLeft "removeKey" $ \r k ->
-		Remote.removeKey r k
+		Remote.removeKey r Nothing k
 	, check isLeft "storeKey" $ \r k -> 
 		Remote.storeKey r k (AssociatedFile Nothing) Nothing nullMeterUpdate
 	, check (`notElem` [Right True, Right False]) "checkPresent" $ \r k ->
@@ -397,7 +397,7 @@ cleanup :: [Remote] -> [Key] -> Bool -> CommandCleanup
 cleanup rs ks ok
 	| all Remote.readonly rs = return ok
 	| otherwise = do
-		forM_ rs $ \r -> forM_ ks (Remote.removeKey r)
+		forM_ rs $ \r -> forM_ ks (Remote.removeKey r Nothing)
 		forM_ ks $ \k -> lockContentForRemoval k noop removeAnnex
 		return ok