Fix for Issue7540 ; urllib2 will raise a TypeError when you try to add_data to
a existing req object already having data.
diff --git a/Lib/urllib2.py b/Lib/urllib2.py
index 122f777..8b26971 100644
--- a/Lib/urllib2.py
+++ b/Lib/urllib2.py
@@ -226,6 +226,9 @@
     # XXX these helper methods are lame
 
     def add_data(self, data):
+        if self.has_data():
+            raise TypeError("Request Obj already contains data: %s" %
+                            self.data)
         self.data = data
 
     def has_data(self):