there is a natural place to initialize `safepri' in a future commit.
Spinoffs:
- spl0() gets called in the unlikely event that isa is not configured.
- configure() has better control over enabling interrupts.
- it is now less unclear that interrupts aren't actually enabled early.
Rev.1.48 of autoconf.c seems to have done the opposite of what was
intended - moving the isa_configure() call delayed the spl0() side
effect.
Added some comments about the bogons. Removed the splhigh() call since
it is a no-op.
cc8ae84672