net/http: correctly show error types in transfer test

actualReader and tc.expectedReader are reflect.Type instance, not the 
actual objects.

So we need to use %s which is gonna call reflect.Type.String and give us 
the 
type name of the readers we are comparing.

src/net/http/transfer_test.go

@@ -267,7 +267,7 @@ func TestTransferWriterWriteBodyReaderTypes(t *testing.T) {
 				}
 
 				if tc.expectedReader != actualReader {
-					t.Fatalf("got reader %T want %T", actualReader, tc.expectedReader)
+					t.Fatalf("got reader %s want %s", actualReader, tc.expectedReader)
 				}
 			}