Load indirect array on demand and flush only on iupdate.

This eliminates all reports of unexpected sharing except a few cases
of honest-to-goodness memory reuse.

Mostly to make sure what I just did works.

This works by lazily allocating a lock's klockstat structure when the
lock is first acquired.

These safety policies help ensure that an accessor does not migrate
CPUs while accessing a percpu variable.  The "cli" safety policy only
allows percpu variables to be accessed when interrupts are disabled.
The "internal" safety policy leaves it up to the caller.  Not
surprisingly, most current percpu variables use internal.

These locks can be statically constructed in the .data segment, since
the constructor is constexpr.  Currently this only works for locks
that aren't tracked by lockstat.

Like the find method of standard containers, this returns an iterator
to the requested key.

I'm sure it fails for some other naming format..

An xns must fit in a page, but that doesn't allow enough buckets
to avoid physical sharing in dirbench.  This is basically a
work-around for the one page limit.