Update NEWS for 1.6.11pre1

Preliminary release notes for OpenAFS 1.6.11

Change-Id: Ibbc9948cd4d8cfc87300f7a7276076af779d37b4
Reviewed-on: http://gerrit.openafs.org/11612
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: D Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>