Re-enable accumulating transfer failure log files for command-line actions

This was disabled in commit 61ccf95004,
because only the assistant used them, and they were clutter. But, now
--failed also uses them.

Remove the failure log files after successful transfers. Should avoid
most of the clutter problems.

Commit 61ccf95004 mentions a subtle behavior
change, which has now been reverted:

    There is one behavior change from this. If glacier is being used, and a
    manual git annex get --from glacier fails because the file isn't available
    yet, the assistant will no longer later see that failed transfer file and
    retry the get.

Annex/Transfer.hs

@@ -94,8 +94,12 @@ runTransfer' ignorelock t file shouldretry transferobserver transferaction = do
 			return observeFailure
 		else do
 			v <- retry info metervar $ transferaction meter
+			let ok = observeBool v
 			liftIO $ cleanup tfile lck
-			transferobserver (observeBool v) t info
+			if ok
+				then removeFailedTransfer t
+				else recordFailedTransfer t info
+			transferobserver ok t info
 			return v
   where
 #ifndef mingw32_HOST_OS

CHANGELOG

@@ -22,6 +22,9 @@ git-annex (6.20160726) UNRELEASED; urgency=medium
     the content is present locally.
   * get, move, copy, mirror: Added --failed switch which retries
     failed copies/moves.
+  * Re-enable accumulating transfer failure log files for command-line
+    actions (disabled in 5.20150522), and remove the log files after
+    successful transfers.
 
  -- Joey Hess <id@joeyh.name>  Wed, 20 Jul 2016 12:03:15 -0400
 

Command/TransferKeys.hs

@@ -35,13 +35,13 @@ start = do
   where
 	runner (TransferRequest direction remote key file)
 		| direction == Upload = notifyTransfer direction file $
-			upload (Remote.uuid remote) key file forwardRetry observer $ \p -> do
+			upload (Remote.uuid remote) key file forwardRetry noObserver $ \p -> do
 				ok <- Remote.storeKey remote key file p
 				when ok $
 					Remote.logStatus remote key InfoPresent
 				return ok
 		| otherwise = notifyTransfer direction file $
-			download (Remote.uuid remote) key file forwardRetry observer $ \p ->
+			download (Remote.uuid remote) key file forwardRetry noObserver $ \p ->
 				getViaTmp (RemoteVerify remote) key $ \t -> do
 					r <- Remote.retrieveKeyFile remote key file t p
 					-- Make sure we get the current
@@ -49,9 +49,6 @@ start = do
 					-- not old cached data.
 					Database.Keys.closeDb			
 					return r
-	
-	observer False t tinfo = recordFailedTransfer t tinfo
-	observer True _ _ = noop
 
 runRequests
 	:: Handle

doc/todo/__34__copy_--failed__34__/comment_1_ff81023df39f9faac5935f6417ad2b38._comment

@@ -3,6 +3,6 @@
  subject="""comment 1"""
  date="2016-08-03T15:07:43Z"
  content="""
-Nice idea, and there's already a log of recent failed transfers that
-could be used.
+Nice idea, and there's already an implementation of a log of recent failed
+transfers that the assistant uses, that can be reused for this.
 """]]