Make sure the interrupt entry point is within the video ROM range. We must
not change interrupt vector if it is not pointing the ROM itself. Actually,
we just fail shadowing altogether if that is the case because the shadowed
copy will be useless for sure and POST may not be relocatable or useful.
While I'm here, fix a debugging message under bootverbose, really. r211829
fixed one case but broke another. Mea Culpa.