New package signing key

A new key has been generated to sign all Lab packages (RPMs and .debs). This has been installed on most Lab managed machines. Private machines which use the Lab repositories will need to register the new key. On a debian based system use "apt-key add" and on an RPM based system use "rpm --import", using the key on the lab web server, e.g. one of: wget -O - http://www.cl.cam.ac.uk/deb/cl.cam.ac.uk-archive-keyring.gpg | sudo apt-key add -; wget -O - www/deb/KEY|sudo apt-key add -; sudo rpm --import http://www.cl.cam.ac.uk/RPM/RPM-GPG-KEY-CL;