Warnings when the config can lead to known errors with delegation

[abompard]

I have tried to do delegation with an Apache config that had GssapiCredStore keytab:/something but no client_keytab nor a ccache set.
As a result of the missing client_keytab, delegation couldn't work, and the missing ccache caused the default ccache to leak.

It would be useful if admins got a warning that they have a setup that will probably not work because it's incomplete or error-prone.