The intent is to get rid of WILLRELE in vnode_if.src by making

The intent is to get rid of WILLRELE in vnode_if.src by making
a complement to all ops that return a vpp, VFS_VRELE.  This is
initially only for file systems that implement the following ops
that do a WILLRELE:

	vop_create, vop_whiteout, vop_mknod, vop_remove, vop_link,
	vop_rename, vop_mkdir, vop_rmdir, vop_symlink

This is initial DNA that doesn't do anything yet.  VFS_VRELE is
implemented but not called.

A default vfs_vrele was created for fs implementations that use the
standard vnode management routines.

VFS_VRELE implementations were made for the following file systems:

Standard (vfs_vrele)
	ffs mfs nfs msdosfs devfs ext2fs

Custom
	union umapfs

Just EOPNOTSUPP
	fdesc procfs kernfs portal cd9660

These implementations may change as VOP changes are implemented.

In the next phase, in the vop implementations calls to vrele and the vrele
part of vput will be moved to the top layer vfs_vnops and made visible
to all layers.  vput will be replaced by unlock in these cases.  Unlocking
will still be done in the per fs layer but the refcount decrement will be
triggered at the top because it doesn't hurt to hold a vnode reference a
little longer.  This will have minimal impact on the structure of the
existing code.

This will only be done for vnode arguments that are released by the various
fs vop implementations.

Wider use of VFS_VRELE will likely require restructuring of the code.

Reviewed by:	phk, dyson, terry et. al.
Submitted by:	Michael Hancock <michaelh@cet.co.jp>