Redmine#2278: linuxmint, ldme, [pure] debian, and [pure] ubuntu hardclasses.

Support for linuxmint, ldme, [pure] debian, and [pure] ubuntu hardclasses.
If linuxmint or ldme, respectfully set ubuntu_derived or debian_derived hardclass.

linuxmint hardclass gets set on both Ubuntu and Debian based Mint Distro; current code requires the following usage:

   Mint Ubuntu Base:  linuxmint.ubuntu_dervied
   Mint Debian Base:  linuxmint.debian_derived or linuxmint.lmde or lmde
   Pure Ubuntu:          ubuntu
   Pure Debian:          debian

Note the above also implies that one cannot simply use linuxmint class alone; which may or may not be desirable. A fix to this would be to alter to code to simply omit defining 'linuxmint' on LMDE systems.