Update NEWS for 1.6.10pre1

Release notes for OpenAFS 1.6.10

Change-Id: I1d5679e375ee442e364c7ee189a316424b7e5d1b
Reviewed-on: http://gerrit.openafs.org/11343
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>