Hashed locking for the namecache

[Andrew Doran <ad%netbsd.org@localhost>]

Hi,

http://www.netbsd.org/~ad/cache.diff

This patch uses a hash of locks to cover forward lookup in the namecache.
On an 8-core box it cuts the time for 'build.sh -j16 release' by about 5%.
We could probably do something a lot more efficient with garbage collection.
But, this patch is simple and I think it could be a stepping stone towards
a more better scheme.

Comments?

Thanks,
Andrew