Make OpenAFS 1.6.8pre2

prerelease for 1.6.8

Change-Id: I1664633e86e218330c729362d5814ec8c160fc5c
Reviewed-on: http://gerrit.openafs.org/10894
Reviewed-by: D Brashear <shadow@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: Stephan Wiesand <stephan.wiesand@desy.de>