docs/162961: [PATCH] Update VirtualBox section in handbook

[Manolis Kiagias]

Here is the latest version of the patch, with few more minor fixes and a 
complete whitespace overhaul:

http://people.freebsd.org/~manolis/patches/virtualization-virtualbox-chapter-patch-new.txt

A test build is here:

http://www.freebsdgr.org/all/en_US.ISO8859-1/books/handbook/virtualization-guest.html

If there are no objections / fixes, this goes in tomorrow :)