* introduces a new filesystem - nfsd.  No, it's not a typo.  It's a small
  tree with fixed topology defined by nfsd and IO on its files does what
  we used to do by hand in nfsctl.c.
* turns sys_nfsservctl() into a sequence of open()/write()/read()/close()
  It works as it used to - we don't need nfsd to be mounted anywhere, etc.
* nfsd_linkage ugliness is gone.
* getfs and getfh demonstrate (rather trivial) example of "descriptor as
  transaction descriptor" behaviour.
* we are fairly close to the situation when driver-defined filesystems can
  be done with practically zero code overhead.  We are still not there, but
  it's a matter of adding a couple of helpers for populating the tree.

	One thing we get immediately is a cleanup of sys_nfsservctl() -
it got _much_ better.  Moreover, we get an alternative interface that
uses normal file IO and can be used without magic syscalls.