VFS messaging/interfacing work stage 2/99. This stage retools the vnode ops

VFS messaging/interfacing work stage 2/99.  This stage retools the vnode ops
vector dispatch, making the vop_ops a per-mount structure rather then a
per-filesystem structure.  Filesystem mount code, typically in blah_vfsops.c,
must now register various vop_ops pointers in the struct mount to compile
its VOP operations set.

This change will allow us to begin adding per-mount hooks to VFSes to support
things like kernel-level journaling, various forms of cache coherency
management, and so forth.

In addition, the vop_*() calls now require a struct vop_ops pointer as the
first argument instead of a vnode pointer (note: in this commit the VOP_*()
macros currently just pull the vop_ops pointer from the vnode in order to
call the vop_*() procedures).  This change is intended to allow us to divorce
ourselves from the requirement that a vnode pointer always be part of a VOP
call.  In particular, this will allow namespace based routines such as
remove(), mkdir(), stat(), and so forth to pass namecache pointers rather then
locked vnodes and is a very important precursor to the goal of using the
namecache for namespace locking.