these changes make the interrupt key available in the
console (before rio is started).
kbdfs: will now send a "interrupt" note to its invoking
process group in cooked mode.
bootrc: is now prepared to handle interrupts, mainly to
not accidently spawn a new bootargs prompt.
init: forwards the interrupt to the cpurc/termrc pgrp.
vncs: shields itself from kbdfs notegroup so interrrupt
wont kill the whole vnc session.
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