Export comerr initialization functions from libafsauthent

Export comerr initialization functions from libafsauthent

Add to the libafsauthent export symbol list these comerr initialization
functions so that they are usable by consumers.

Change-Id: I72c6f9402a46aff6fa2719c0b9e0974c7ff7b57e
Reviewed-on: https://gerrit.openafs.org/13055
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Anders Kaseorg <andersk@mit.edu>
Tested-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>