Update support versions

We support:
 * The oldest regular lifecycle RHEL
 * The long term support release, if any, of the four major desktop distros
 * The current release of the four major desktop distros

Six months ago this meant:
 * RHEL5
 * Ubuntu 10.04 and Debian 6
 * Ubuntu 11.10, Fedora 16, and openSUSE 12.1

but this is now out of date. Update and re-qualify. As at 2012-09, Michael thinks this means:
 * RHEL5, and add RHEL6
 * Ubuntu 10.04, 12.04, and Debian 6
 * Ubuntu 12.04, Fedora 17, and openSUSE 12.2

Michael wants to keep Ubuntu 10.04 support until 12.04 is properly established.