Forward port from Zope 2.7 branch.

The ConflictError.get_{old,new}_serial() methods each did what the other
was supposed to do.

NEWS.txt

@@ -68,6 +68,13 @@ before, it now says:
     serial this txn started with 0x034414228c3728d5 2002-04-14 20:50:32.863000,
     serial currently committed 0x03441422948b4399 2002-04-14 20:50:34.815000)
 
+ConflictError
+-------------
+
+The undocumented ``get_old_serial()`` and ``get_new_serial()`` methods
+were swapped (the first returned the new serial, and the second returned
+the old serial).
+
 Tools
 -----
 

src/ZODB/POSException.py

@@ -112,10 +112,10 @@ class ConflictError(TransactionError):
         return self.class_name
 
     def get_old_serial(self):
-        return self.serials[0]
+        return self.serials[1]
 
     def get_new_serial(self):
-        return self.serials[1]
+        return self.serials[0]
 
     def get_serials(self):
         return self.serials