Comment 6 for bug 1308378

If an admin does rm /etc/resolv.conf on the 14.04, name resolving stops working and no upgrade will undo that change, since the preinst check is only there when upgrading from the 12.04's version of the package. This can also be tested by installing the new package multiple times, removing resolv.conf in between - it does not get back in that case, because the upgrade) is called with the 1.69 version which is higher than what's checked.

If admin does rm /etc/resolv.conf in 12.04, name resolving continues to work because the name resolving does not stop working at that like it does on 14.04 (possibly because /run/resolvconf/resolv.conf is always watched in 12.04 instead or some other detail that has changed?). If the system is then upgraded to 14.04, either: a) without this fix name resolving will simply stop working, because of the difference in behavior in 14.04, b) with this fix the symlink gets reinstated and name resolving continues to work after the upgrade.