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.

diff --cc Misc/ACKS
Simple merge

diff --cc Misc/NEWS
index 9774f1552437f1a7549a5a20775dc1cb46df28d6,f3442a52bbbb44e5f5ab3ce81c00c79077ff6003..483e6607e95a30a1d3d6b28fb2e9eb584b1bdf31
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -68,9 -34,10 +68,13 @@@ Core and Builtin
  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 #1162477: Postel Principal adjustment to email date parsing: handle the
 +  fact that some non-compliant MUAs use '.' instead of ':' in time specs.
 +
  - Issue #11131: Fix sign of zero in decimal.Decimal plus and minus
    operations when the rounding mode is ROUND_FLOOR.