(MESS) megacd.xml: logged data of the original bin+cue used for creating
CHDs. this shall be of help to remove bad dumps or keep good ones
when redumps become available. while at it, removed outdated note at top
(Euro system does recognize discs in current tree) and added ring codes
when available (allowing for the removal of a bunch of disks sourced
from iso+wav, when better source were available) nw.