+ xref closes with '/>'. This causes a trailing '>'

at the end of the reference.  Removed the '/'.

+ Marked up 'log' and 'spool' as filenames

in the discussion of the 'var' directory.

+ Changed fdisk to show up as command.

+ Marked up vn as device.

+ Marked up "sysinstall" using a man.systinstall.8; entity.

PR: docs/28989
Submitted by: Martin Heinen <mheinen0@wiesbaden-online.de>