make bytes(o) respect __bytes__ #2415

This adds two new C-API functions: PyObject_Bytes and PyBytes_FromObject.

Reviewer: Barry
diff --git a/Include/bytesobject.h b/Include/bytesobject.h
index ece06d2..3f275a8 100644
--- a/Include/bytesobject.h
+++ b/Include/bytesobject.h
@@ -48,6 +48,7 @@
 
 PyAPI_FUNC(PyObject *) PyBytes_FromStringAndSize(const char *, Py_ssize_t);
 PyAPI_FUNC(PyObject *) PyBytes_FromString(const char *);
+PyAPI_FUNC(PyObject *) PyBytes_FromObject(PyObject *);
 PyAPI_FUNC(PyObject *) PyBytes_FromFormatV(const char*, va_list)
 				Py_GCC_ATTRIBUTE((format(printf, 1, 0)));
 PyAPI_FUNC(PyObject *) PyBytes_FromFormat(const char*, ...)