accounting: Make checkers show what they are doing

Before this change, all types of checkers showed "checking" after the
file name despite the fact that not all of them were checking.

After this change, they can show

- checking
- deleting
- hashing
- importing
- listing
- merging
- moving
- renaming

See: https://forum.rclone.org/t/what-is-rclone-checking-during-a-purge/35931/

fs/sync/sync.go

@@ -329,7 +329,7 @@ func (s *syncCopyMove) pairChecker(in *pipe, out *pipe, fraction int, wg *sync.W
 		}
 		src := pair.Src
 		var err error
-		tr := accounting.Stats(s.ctx).NewCheckingTransfer(src)
+		tr := accounting.Stats(s.ctx).NewCheckingTransfer(src, "checking")
 		// Check to see if can store this
 		if src.Storable() {
 			needTransfer := operations.NeedTransfer(s.ctx, pair.Dst, pair.Src)
@@ -779,7 +779,7 @@ func (s *syncCopyMove) makeRenameMap() {
 			for obj := range in {
 				// only create hash for dst fs.Object if its size could match
 				if _, found := possibleSizes[obj.Size()]; found {
-					tr := accounting.Stats(s.ctx).NewCheckingTransfer(obj)
+					tr := accounting.Stats(s.ctx).NewCheckingTransfer(obj, "renaming")
 					hash := s.renameID(obj, s.trackRenamesStrategy, s.modifyWindow)
 
 					if hash != "" {