Update NEWS for 1.6.2.1

Change-Id: I2c08474cc6034d40cef0d77d94c070bcdd8d4563
Reviewed-on: http://gerrit.openafs.org/9602
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>