MFbed: Update the German documentation set.

doc/de_DE.ISO8859-1/books/handbook/Makefile 1.102 -> 1.103
doc/de_DE_ISO8859-1/books/handbook/advanced-networking/chapter.sgml 1.389 -> 1.396
doc/de_DE.ISO8859-1/books/handbook/firewalls/chapter.sgml 1.74 -> 1.75
doc/de_DE.ISO8859-1/books/handbook/virtualization/chapter.sgml new translation [X]

Obtained from: The FreeBSD German Documentation Project.

• Contributed/translated by: Oliver Peter (hoschi at mouhaha dot de)