for kernel code which has been written to avoid MP contention by
using cpu-local storage (most prominently, select and pool_cache).
Instead of always assuming rump_cpu, the scheduler must now be run
(and unrun) on all entry points into rump. Likewise, rumpuser
unruns and re-runs the scheduler around each potentially blocking
operation. As an optimization, I modified some locking primitives
to try to get the lock without blocking before releasing the cpu.
Also, ltsleep was modified to assume that it is never called without
the biglock held and made to use the biglock as the sleep interlock.
Otherwise there is just too much drama with deadlocks. If some
kernel code wants to call ltsleep without the biglock, then, *snif*,
it's no longer supported and rump and should be modified to support
newstyle locks anyway.
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