archive/tar: fix error message

Write should return ErrWriteAfterClose instead
of ErrWriteTooLong when called after Close.

Change-Id: If5ec4ef924e4c56489e0d426976f7e5fad79be9b
Reviewed-on: https://go-review.googlesource.com/9259Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/archive/tar/writer.go

@@ -355,7 +355,7 @@ func paxHeader(msg string) string {
 // hdr.Size bytes are written after WriteHeader.
 func (tw *Writer) Write(b []byte) (n int, err error) {
 	if tw.closed {
-		err = ErrWriteTooLong
+		err = ErrWriteAfterClose
 		return
 	}
 	overwrite := false

src/archive/tar/writer_test.go

@@ -489,3 +489,20 @@ func TestValidTypeflagWithPAXHeader(t *testing.T) {
 		}
 	}
 }
+
+func TestWriteAfterClose(t *testing.T) {
+	var buffer bytes.Buffer
+	tw := NewWriter(&buffer)
+
+	hdr := &Header{
+		Name: "small.txt",
+		Size: 5,
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		t.Fatalf("Failed to write header: %s", err)
+	}
+	tw.Close()
+	if _, err := tw.Write([]byte("Kilts")); err != ErrWriteAfterClose {
+		t.Fatalf("Write: got %v; want ErrWriteAfterClose", err)
+	}
+}