Backport fast alternate io.BytesIO implementation.
Merged r62778, r62779, r62802, r62806, r62807, r62808, r62809, r62844,
r62846, r62952, r62956.
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index 542f266..3b52147 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -315,8 +315,8 @@
     Py_buffer vo;
 
     if (_getbuffer(other, &vo) < 0) {
-        PyErr_Format(PyExc_TypeError, "can't concat bytes to %.100s",
-                     Py_TYPE(self)->tp_name);
+        PyErr_Format(PyExc_TypeError, "can't concat %.100s to %.100s",
+                     Py_TYPE(other)->tp_name, Py_TYPE(self)->tp_name);
         return NULL;
     }