Fix #11491. When dbm.open was called with a file which already exists and

the "flag" argument is "n", dbm.error was being raised. As documented,
dbm.open(...,flag='n') will now "Always create a new, empty database,
open for reading and writing", regardless of a previous file existing.

Misc/ACKS

@@ -154,6 +154,7 @@ Terrence Cole
 Benjamin Collar
 Jeffery Collins
 Paul Colomiets
+Denver Coneybeare
 Matt Conway
 David M. Cooke
 Greg Copeland

Misc/NEWS

@@ -40,6 +40,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #11491: dbm.error is no longer raised when dbm.open is called with
+  the "n" as the flag argument and the file exists. The behavior matches
+  the documentation and general logic.
+   
 - Issue #11131: Fix sign of zero in decimal.Decimal plus and minus
   operations when the rounding mode is ROUND_FLOOR.