Prepare 3.1.3 release

CHANGES.txt

@@ -1,5 +1,5 @@
-3.1.3 (Next 3.x Release)
-------------------------
+3.1.3 (2014-10-28)
+------------------
 
 - Fixed an XML-RPC bug where the ElementTree-based parser handled strings
   like ``<value><string>hello</string></value>`` but not strings like

supervisor/version.txt

@@ -1 +1 @@
-3.1.2
+3.1.3