display scanning message whenever reconcileStaged has enough files to chew on

Clear visible progress bar first.

Removed showSideActionAfter because it can't be used in reconcileStaged
(import loop). Instead, it counts the number of files it
processes and displays it after it's seen a sufficient to know it's
taking a while.

Sponsored-by: Dartmouth College's Datalad project

Utility/Metered.hs

@@ -425,7 +425,8 @@ displayMeterHandle h rendermeter v msize old new = do
 		hPutStr h ('\r':s ++ padding)
 		hFlush h
 
--- | Clear meter displayed by displayMeterHandle.
+-- | Clear meter displayed by displayMeterHandle. May be called before
+-- outputting something else, followed by more calls to displayMeterHandle.
 clearMeterHandle :: Meter -> Handle -> IO ()
 clearMeterHandle (Meter _ _ v _) h = do
 	olds <- readMVar v