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.

I'll be changing the dirns implementation soon.

..next step is a namex that takes no refs.

The only unexpected sharing is on the VMA refcount, which is
exactly what we expected.

This eliminates a bunch of confusing scopes that come from thread creation

With the mtrace QEMU, which now switches VCPUs when there's a PAUSE,
this speeds up my lame test (usertests vmoverlap) by a factor of 7 and
certainly makes xv6 feel much faster.

So we can hush up spurious errors.

The user errors stream is disabled by default.

These have the type-safety and extensibility of ostreams, but the
simplicity and almost the terseness of printf.

Split the inode space into per-cpu spaces of size IPB that start at
the begining of a block.  Block awareness is important to avoid
contention on blocks themselves when allocating or freeing an inode
and updating on-disk structures.  That is, I don't want to make bio
scalable.