Debian build fix

The first commit updates radiusd-to-freeradius.diff so it applies cleanly without fuzz (required when debian/source/format - 3.0 (quilt)). This change tested to build fine for ubuntu precise and trusty on https://launchpad.net/~freeradius/+archive/testing-3.x 


The second and third commit changes required debhelper to (>= 7.4) to enable build on oldest supported Ubuntu LTS (lucid/10.04, debhelper 7.4.15ubuntu1) and debian oldstable (squeeze, debhelper 8.0.0). This change (plus the previous one) is tested to build fine for ubuntu lucid on the same ppa (build log for lucid available on https://launchpadlibrarian.net/175885521/buildlog_ubuntu-lucid-amd64.freeradius_3.1.0~git~20140518~1~fb31b78-ppa3~lucid_UPLOADING.txt.gz)