Linux Training updates

Linux Training got a lot of updates the past two weeks (thank you financial crisis for giving me time).

Added an introduction to mysql (chapter 31 in LinuxTraining.pdf). (Can someone with mysql knowledge please review this ?)

Finally updated init and booting, they are two chapters now. Booting is chapter 17, init is chapter 18. The practices for these chapters are not done yet, and lilo could use a bit more info.

Notes to self:
- chapter 13 (more about bash) is dreadful, high priority!
- idem ditto for 22.scheduling and 24.memory management

By the way, there is really no point in putting old copies of this book online (like on scribd). The latest complete version can always be downloaded at www.linux-training.be.