ABS guide: convert the whole book sources to Docbook/XML 4.5
ABS guide: make some self references in command example link to *.xml document.
ABS guide: Fix {sgml -> xml} in docbook comment
Merge pull request #1 from Fat-Zer/abs-xml

ABS Docbook/xml conversion, thanks to Fat-Zer
du.sh was renamed to Du.sh but the old file is steal present.