Whine if single-DES keys are in use

If we are using single-DES keys in our KeyFile, yell at the
administrator, so they have a chance at realizing that they should
migrate to stronger crypto.

Reviewed-on: http://gerrit.openafs.org/10273
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 4212c7e604bebcb8f20b67c60323263231611bfb)

Change-Id: I00b47889e7e79819a3c5d347349686e5d2da30e8
Reviewed-on: http://gerrit.openafs.org/10274
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>