Give the VFS initialisation functions an update:

Give the VFS initialisation functions an update:

	* Use a better fix for revision 1.3 of vfs_init.c (ours).
	  I have integrated the change from FreeBSD's vfs_init.c
	  revision 1.59.  Serious issues are fixed with this
	  change and a much more cleaner way of handling disappearing
	  VFS operation vectors.  At least vfs_opv_numops are
	  allocated and recycled as appropriate.  The number of
	  pre-allocated vfs_opv_numops can be changed at boot time
	  by a tunable.  $FreeBSD$ ID tag updated accordingly.

	  NOTE: this *removes* the temporary fix committed my dillon@
	  a few days ago, by giving it a more cleaner solution.

	* Use M_VNODE instead of M_TEMP for storing VFS buffers and
	  vectors.

	* Document the functions in this file to make it easier
	  for file system implementors.

	* Cleanup unused variables in vfs_add_vnops().

	* Use M_ZERO instead of malloc+bzero.

	* Do not panic when a VFS operation is not available,
	  instead return EOPNOTSUPP.  This is better because
	  the error value can be passed up by the system calls
	  instead of giving an obscure panic about unavailable
	  VFS operation.  One can run into this when a VFS op
	  call is made when no filesystem supports that
	  particular op.  A similar change was made by Peter
	  Wemm in FreeBSD's sys/kern/vfs_init.c.

	* Better document the various stages of vfs_opv_recalc().

Note, our value of the minimum number of available VFS operation
vectors is `96' at the moment, since a few tests show that the
previous code initialised to values of between 53-60.  The default
probably can be tuned a little bit better; although tunable access
is available at boot to `vfs.opv_numops'.

Reviewed by:	Matt Dillon