spl0) and some bitrot (the not-so-new callout_init/stop/reset functions
were not mentioned; the callout_activate/deactivate/pending macros are
still not mentioned).
Submitted by: mostly by jlemon
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.