Import NEWS from openafs-stable-1_6_x

Import NEWS from openafs-stable-1_6_x

The 1.6.x changelog entries have been going directly on the
openafs-stable-1_6_x branch for ease of maintenance.

However, we don't want to skip those changes when mentioning changes
in OpenAFS 1.8, so pull back a copy onto master before adding
things for 1.8.

Change-Id: I545c19db9854300a84295d3ca8b1f301756c38b0
Reviewed-on: https://gerrit.openafs.org/12392
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>