Replace reference from vinum.8 to gvinum.8, it was advised in the PR to

replace this with vinum.4, but that's the kernel interface manual, which
is not appropriate in my understanding.  I think that gvinum is a suitable
replacement for this.

PR:		docs/121938
Submitted by:	"Federico" <federicogalvezdurand at yahoo dot com>
MFC after:	3 days

sbin/newfs/newfs.8

@@ -28,7 +28,7 @@
 .\"     @(#)newfs.8	8.6 (Berkeley) 5/3/95
 .\" $FreeBSD$
 .\"
-.Dd January 21, 2005
+.Dd March 21, 2008
 .Dt NEWFS 8
 .Os
 .Sh NAME
@@ -268,7 +268,7 @@ on file systems that contain many small files.
 .Xr fsck 8 ,
 .Xr mount 8 ,
 .Xr tunefs 8 ,
-.Xr vinum 8
+.Xr gvinum 8
 .Rs
 .%A M. McKusick
 .%A W. Joy