other semantics from an earlier incarnation.
Call kcont_init() from init_main before device autoconfiguration,
so kcont is availble to device drivers if required.
Also ensure the kthread process runs any pending continuations once
the kthread is finally up and running. For now, use a non-null timeout
to poll the queue periodically. Draining any pending requests just
before the kthread enters its ltsleep()/kc_run loop is cleaner, but
this is the version I tested with an early-in-boot kcont request.)
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