Use go-winio tar-application code instead of our own

applyFunc now takes an io.Reader instead of a tar.Reader because I'm
trying to mirror the API of the not-yet-exposed implementation of this
same behaviour in github.com/Microsoft/hcsshim/internal/ociwclayer,
with an eye to later moving to that implementation it is ever exposed.

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>

archive/tar.go

@@ -114,16 +114,18 @@ func Apply(ctx context.Context, root string, r io.Reader, opts ...ApplyOpt) (int
 		options.applyFunc = applyNaive
 	}
 
-	return options.applyFunc(ctx, root, tar.NewReader(r), options)
+	return options.applyFunc(ctx, root, r, options)
 }
 
 // applyNaive applies a tar stream of an OCI style diff tar to a directory
 // applying each file as either a whole file or whiteout.
 // See https://github.com/opencontainers/image-spec/blob/master/layer.md#applying-changesets
-func applyNaive(ctx context.Context, root string, tr *tar.Reader, options ApplyOptions) (size int64, err error) {
+func applyNaive(ctx context.Context, root string, r io.Reader, options ApplyOptions) (size int64, err error) {
 	var (
 		dirs []*tar.Header
 
+		tr = tar.NewReader(r)
+
 		// Used for handling opaque directory markers which
 		// may occur out of order
 		unpackedPaths = make(map[string]struct{})