As discussed on python-dev, add a mechanism to indicate features
that are in the process of deprecation (PendingDeprecationWarning).
Docs could be improved.
diff --git a/Lib/warnings.py b/Lib/warnings.py
index 435f1a7..fc6154f 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -262,3 +262,4 @@
 else:
     _processoptions(sys.warnoptions)
     filterwarnings("ignore", category=OverflowWarning, append=1)
+    filterwarnings("ignore", category=PendingDeprecationWarning, append=1)