Better errors from aklog

Better errors from aklog

Since the great com_err fracture, aklog has only returned decent
error messages from AFS, leaving Kerberos errors untranslated.
Needless to say, this causes user confusion and distress.

This patch uses the error display proc hook to call out to the real
com_err in situations where AFS can't supply an error message, giving
clearer errors for Kerberos problems.

Change-Id: I8832b755beb84c593e1b2eace5c356e71a582b2a
Reviewed-on: http://gerrit.openafs.org/821
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>