Log Message:
PKG_OPTIONize kerberos as 'kerberos'. From: Matthias Kretschmer via PR#45823
with a minor edit.
N.B.: a minority of packages uses 'gssapi' as the option name. We should
decide on one option name and fix all packages to use the same, with
notification of the users and a transition mechanism. (Do we support, or
intend to support, any GSSAPI mechanisms other than Kerberos? In parallel?)