Bug#891976: reported in Ubuntu as well

A corresponding Ubuntu bug report: https://bugs.launchpad.net/ubuntu/+source/base-installer/+bug/1298924

Bug#891976: it does screw up C.UTF-8 immediately

While it does no much harm at first if you select C during installation, it immediately screws up C.UTF-8 selected during installation. In that case the installer still adds the lines above without any warning, therefore if root logs in, he gets C insead of C.UTF-8. Good luck for finding these