[Tutor] Database topic now fixed

[Alan Gauld]

> Some observations:

These have now all been addressed as previously discussed.

I've also added a section at the end covering the use of execute() to
insert parameters rather than relying on format strings since the
latter can be a security risk.

Hopefully its now complete! :-)

Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld