webapp: Progess bar fixes for many types of special remotes.

There was confusion in different parts of the progress bar code about
whether an update contained the total number of bytes transferred, or the
number of bytes transferred since the last update. One way this bug
showed up was progress bars that seemed to stick at zero for a long time.
In order to fix it comprehensively, I add a new BytesProcessed data type,
that is explicitly a total quantity of bytes, not a delta.

Note that this doesn't necessarily fix every problem with progress bars.
Particularly, buffering can now cause progress bars to seem to run ahead
of transfers, reaching 100% when data is still being uploaded.

Remote/Git.hs

@@ -40,6 +40,7 @@ import Init
 import Types.Key
 import qualified Fields
 import Logs.Location
+import Utility.Metered
 
 import Control.Concurrent
 import Control.Concurrent.MSampleVar
@@ -309,7 +310,7 @@ copyFromRemote r key file dest
 			: maybe [] (\f -> [(Fields.associatedFile, f)]) file
 		Just (cmd, params) <- git_annex_shell (repo r) "transferinfo" 
 			[Param $ key2file key] fields
-		v <- liftIO $ newEmptySV
+		v <- liftIO $ (newEmptySV :: IO (MSampleVar Integer))
 		tid <- liftIO $ forkIO $ void $ tryIO $ do
 			bytes <- readSV v
 			p <- createProcess $
@@ -325,7 +326,7 @@ copyFromRemote r key file dest
 			send bytes
 			forever $
 				send =<< readSV v
-		let feeder = writeSV v
+		let feeder = writeSV v . fromBytesProcessed
 		bracketIO noop (const $ tryIO $ killThread tid) (a feeder)
 
 copyFromRemoteCheap :: Remote -> Key -> FilePath -> Annex Bool
@@ -391,13 +392,13 @@ rsyncOrCopyFile rsyncparams src dest p =
 	dorsync = rsyncHelper (Just p) $
 		rsyncparams ++ [Param src, Param dest]
 	docopy = liftIO $ bracket
-		(forkIO $ watchfilesize 0)
+		(forkIO $ watchfilesize zeroBytesProcessed)
 		(void . tryIO . killThread)
 		(const $ copyFileExternal src dest)
 	watchfilesize oldsz = do
 		threadDelay 500000 -- 0.5 seconds
 		v <- catchMaybeIO $
-			fromIntegral . fileSize
+			toBytesProcessed . fileSize
 				<$> getFileStatus dest
 		case v of
 			Just sz