Current policy mandates that directories in /usr/local should be owned
by group staff and mode 2775.

The purpose of this file is to tell the system, when it's removed, that we
want directories in /usr/local to be 755 and owned by group root.

At this moment, this does not work at all, but the plan is to modify
packages during the development stage of wheezy+1, so that whenever we
release wheezy+1 as stable, all packages that need it check that this
file exists before using those special permissions for /usr/local.

This file is created by base-files on the initial install, and it's
also created on upgrades from any base-files release before 6.10, which
means it will be created on upgrades from squeeze to wheezy.

See https://bugs.debian.org/299007 for details.