Issue #3139: Make buffer-interface thread-safe wrt. PyArg_ParseTuple,
by denying s# to parse objects that have a releasebuffer procedure,
and introducing s*.

More module might need to get converted to use s*.
diff --git a/Include/object.h b/Include/object.h
index c00df74..6c04034 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -162,7 +162,8 @@
 /* Py3k buffer interface */
 
 typedef struct bufferinfo {
-	void *buf;         
+	void *buf;   
+	PyObject *obj;        /* borrowed reference */
         Py_ssize_t len;
         Py_ssize_t itemsize;  /* This is Py_ssize_t so it can be 
                                  pointed to by strides in simple case.*/