pending adds now retried for kqueue

Rethought how to keep track of pending adds that need to be retried later.
The commit thread already run up every second when there are changes,
so let's keep pending adds queued as changes until they're safe to add.

Also, the committer is now smarter about avoiding empty commits when
all the adds are currently unsafe, or in the rare case that an add event
for a symlink is not received in time. It may avoid them entirely.

This seems to work as before for inotify, and is untested for kqueue.

(Actually commit batching seems to be improved for inotify, although I'm
not sure why. I'm seeing only two commits made during large batch
operations, and the first of those is the non-batch mode commit.)

Assistant/Changes.hs

@@ -7,20 +7,26 @@ module Assistant.Changes where
 
 import Common.Annex
 import qualified Annex.Queue
+import Types.KeySource
 
 import Control.Concurrent.STM
 import Data.Time.Clock
 
-data ChangeType = PendingAddChange | LinkChange | RmChange | RmDirChange
+data ChangeType = AddChange | LinkChange | RmChange | RmDirChange
 	deriving (Show, Eq)
 
 type ChangeChan = TChan Change
 
-data Change = Change
-	{ changeTime :: UTCTime
-	, changeFile :: FilePath
-	, changeType :: ChangeType
-	}
+data Change
+	= Change 
+		{ changeTime :: UTCTime
+		, changeFile :: FilePath
+		, changeType :: ChangeType
+		}
+	| PendingAddChange
+		{ changeTime ::UTCTime
+		, keySource :: KeySource
+		}
 	deriving (Show)
 
 runChangeChan :: STM a -> IO a
@@ -33,13 +39,29 @@ newChangeChan = atomically newTChan
 madeChange :: FilePath -> ChangeType -> Annex (Maybe Change)
 madeChange f t = do
 	-- Just in case the commit thread is not flushing the queue fast enough.
-	when (t /= PendingAddChange) $
-		Annex.Queue.flushWhenFull
+	Annex.Queue.flushWhenFull
 	liftIO $ Just <$> (Change <$> getCurrentTime <*> pure f <*> pure t)
 
 noChange :: Annex (Maybe Change)
 noChange = return Nothing
 
+{- Indicates an add is in progress. -}
+pendingAddChange :: KeySource -> Annex (Maybe Change)
+pendingAddChange ks =
+	liftIO $ Just <$> (PendingAddChange <$> getCurrentTime <*> pure ks)
+
+isPendingAddChange :: Change -> Bool
+isPendingAddChange (PendingAddChange {}) = True
+isPendingAddChange _ = False
+
+finishedChange :: Change -> Change
+finishedChange c@(PendingAddChange { keySource = ks }) = Change
+	{ changeTime = changeTime c
+	, changeFile = keyFilename ks
+	, changeType = AddChange
+	}
+finishedChange c = c
+
 {- Gets all unhandled changes.
  - Blocks until at least one change is made. -}
 getChanges :: ChangeChan -> IO [Change]