Issue #4258:  Make it possible to use 30-bit digits for PyLongs:
 - new configure option --enable-big-digits
 - new structseq sys.int_info giving information about the internal format
By default, 30-bit digits are enabled on 64-bit machines but
disabled on 32-bit machines.
diff --git a/Include/longobject.h b/Include/longobject.h
index 7adf9c7..28fb707 100644
--- a/Include/longobject.h
+++ b/Include/longobject.h
@@ -26,6 +26,7 @@
 PyAPI_FUNC(size_t) PyLong_AsSize_t(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLong(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLongMask(PyObject *);
+PyAPI_FUNC(PyObject *) PyLong_GetInfo(void);
 
 /* It may be useful in the future. I've added it in the PyInt -> PyLong
    cleanup to keep the extra information. [CH] */