Update NEWS for 1.6.6pre2

release notes for OpenAFS 1.6.6 prerelease 2

Change-Id: Id829b60e82d56d11ebfb454595518d9585ca63fe
Reviewed-on: http://gerrit.openafs.org/10596
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>