oops, actually define MARK_RAMDISK?

forgot to commit this... rebase needed! :)
fix 56a6c381d1b7c2afca16a979874b4ee9c77d2b89

leave maxp undisturbed (and thus MARK_END/esym)
fix and enhance comment describing kernel layout

ok hshoexer@genua
fix 7b9e226cd2e130f656092d0eab346d1b271d6dae
silly printf