Warn against sorting requirements

Mark pbr/hacking as first projects.

For background see mail thread starting at:
http://lists.openstack.org/pipermail/openstack-dev/2014-September/044736.html

Change-Id: I64ae9191863564e278a35d42ec9cd743a233028e
Closes-Bug: 1365061
Merge "Warn against sorting requirements"