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

Types/Messages.hs

@@ -47,6 +47,7 @@ data MessageState = MessageState
 	, consoleRegionErrFlag :: Bool
 	, jsonBuffer :: Maybe Aeson.Object
 	, promptLock :: MVar () -- left full when not prompting
+	, clearProgressMeter :: IO ()
 	}
 
 newMessageState :: IO MessageState
@@ -60,6 +61,7 @@ newMessageState = do
 		, consoleRegionErrFlag = False
 		, jsonBuffer = Nothing
 		, promptLock = promptlock
+		, clearProgressMeter = return ()
 		}
 
 -- | When communicating with a child process over a pipe while it is