Use "pack file" instead of "data file" (#2885)

- changed variable names, especially changed DataFile into PackFile
- changed in some comments
- always use "pack file" in docu

internal/checker/checker.go

@@ -236,7 +236,7 @@ func (c *Checker) Packs(ctx context.Context, errChan chan<- error) {
 	debug.Log("listing repository packs")
 	repoPacks := restic.NewIDSet()
 
-	err := c.repo.List(ctx, restic.DataFile, func(id restic.ID, size int64) error {
+	err := c.repo.List(ctx, restic.PackFile, func(id restic.ID, size int64) error {
 		repoPacks.Insert(id)
 		return nil
 	})
@@ -701,7 +701,7 @@ func (c *Checker) GetPacks() restic.IDSet {
 // checkPack reads a pack and checks the integrity of all blobs.
 func checkPack(ctx context.Context, r restic.Repository, id restic.ID) error {
 	debug.Log("checking pack %v", id)
-	h := restic.Handle{Type: restic.DataFile, Name: id.String()}
+	h := restic.Handle{Type: restic.PackFile, Name: id.String()}
 
 	packfile, hash, size, err := repository.DownloadAndHash(ctx, r.Backend(), h)
 	if err != nil {

internal/checker/checker_test.go

@@ -82,7 +82,7 @@ func TestMissingPack(t *testing.T) {
 	repo := repository.TestOpenLocal(t, repodir)
 
 	packHandle := restic.Handle{
-		Type: restic.DataFile,
+		Type: restic.PackFile,
 		Name: "657f7fb64f6a854fff6fe9279998ee09034901eded4e6db9bcee0e59745bbce6",
 	}
 	test.OK(t, repo.Backend().Remove(context.TODO(), packHandle))