avoid calling the progress callback when the bytes sent have not changed

Does rsync stall and update its progress display? Dunno, but this was an
easy optimisation to throw in.

Utility/Rsync.hs

@@ -54,10 +54,10 @@ rsync = boolSystem "rsync"
  -}
 rsyncProgress :: (Integer -> IO ()) -> [CommandParam] -> IO Bool
 rsyncProgress callback params = catchBoolIO $
-	withHandle StdoutHandle createProcessSuccess p (feedprogress [])
+	withHandle StdoutHandle createProcessSuccess p (feedprogress 0 [])
 	where
 		p = proc "rsync" (toCommand params)
-		feedprogress buf h = do
+		feedprogress prev buf h = do
 			s <- hGetSomeString h 80
 			if null s
 				then return True
@@ -65,8 +65,12 @@ rsyncProgress callback params = catchBoolIO $
 					putStr s
 					hFlush stdout
 					let (mbytes, buf') = parseRsyncProgress (buf++s)
-					maybe noop callback mbytes
-					feedprogress buf' h
+					case mbytes of
+						Nothing -> feedprogress prev buf' h
+						(Just bytes) -> do
+							when (bytes /= prev) $
+								callback bytes
+							feedprogress bytes buf' h
 
 {- Checks if an rsync url involves the remote shell (ssh or rsh).
  - Use of such urls with rsync requires additional shell