MFde: Update the german handbook.

Resync multiple handbook chapters with the latest version.

books/handbook/audit/chapter.sgml 1.33 -> 1.34
books/handbook/boot/chapter.sgml 1.65 -> 1.70
books/handbook/introduction/chapter.sgml 1.136 -> 1.137
books/handbook/l10n/chapter.sgml 1.129 -> 1.131 [1]
books/handbook/mirrors/chapter.sgml 1.464 -> 1.474

[1] Contributed by: Frank Boerner (frank dash freebsd at online dot de)
Obtained from: The FreeBSD German Documentation Project