[rfc] init: warn on obvious KERNEL/SYSTEM mismatch

... because rpi / netboot users still cant get it

and I am tired of reports like [this](http://openelec.tv/forum/71-pvr-live-tv/73856-tvheadend-unreachable#123133) and to explain it [again](http://openelec.tv/forum/71-pvr-live-tv/73856-tvheadend-unreachable#123144) and [again](http://openelec.tv/forum/124-raspberry-pi/46413-howto-install-openelec-on-raspberry-pi-on-a-tiny-sd-and-a-1gb-usb-drive?start=15#123141)

quick and ditry. needs runtime testing. I am not going to. and arguments like "we want evenmoresilent boot" are invalid, so please dont.