Should be able to handle more than one book

This module is exactly what I was looking for, for my site! With one difference: I have mutliple books on the site, so don't want to be restricted to using the module with one book only.
So, I attach a patch. It contains the following differences:

1. You can use arguments on the URL to decide which book to open and how deep: for example, "booktree/45/5" will display book node 45 and its children to a depth of 5 (if you don't use arguments then it will use the default configuration as now).
2. Instead of displaying the module name as the page title, it displays the Book title (top level: in our example, the page title will be the title of node/45).
3. It no longer displays the title of the starting node within the page (this didn't seem very useful somehow)
4. And I also commented out the first sql statement which didn't seem to serve any useful purpose

Note that this is tested only for 5.1 - if Uccio would like to take this over and incorporate it, that would be great.