Expose Py_Py3kWarningFlag as sys.py3kwarning as discussed in #1504
Also added a warning.warnpy3k() as convenient method for Python 3.x related deprecation warnings.
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 774a7db..617c38a 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -1167,6 +1167,8 @@
PyString_FromString(Py_GetExecPrefix()));
SET_SYS_FROM_STRING("maxint",
PyInt_FromLong(PyInt_GetMax()));
+ SET_SYS_FROM_STRING("py3kwarning",
+ PyBool_FromLong(Py_Py3kWarningFlag));
#ifdef Py_USING_UNICODE
SET_SYS_FROM_STRING("maxunicode",
PyInt_FromLong(PyUnicode_GetMax()));