[$] Systemd discusses its kernel-version needs

A query regarding the possibility of dropping support for older kernels in systemd ledto some discussion on the systemd-devel mailing list recently. As might beguessed, exactly which kernel would be the minimumsupported, what kernel features systemd is using, and when those kernelfeatures became available, were all part of that conversation.A component like systemd that is closely tied to the kernel, and the interfacesdifferent versionsprovide, has a number of different factors to consider when making adecision of this sort.