I have no idea what happened; manual setting of localtime to UTC (command below) fixed the configuration of the package, allowing the upgrade to continue.
Anyway, I executed the following command to set to UTC, and then proceeded to complete the dist-upgrade from 15.05, and the error from tzdata was resolved; I'll fix my timezone after the upgrade completes.
So,
I have no idea what happened; manual setting of localtime to UTC (command below) fixed the configuration of the package, allowing the upgrade to continue.
Anyway, I executed the following command to set to UTC, and then proceeded to complete the dist-upgrade from 15.05, and the error from tzdata was resolved; I'll fix my timezone after the upgrade completes.
#ln -sf /usr/share/ zoneinfo/ UTC /etc/localtime