Tutorial example errors

[Edward Diener <eld@…>]

In the tutorial for Boost parameter there are a number of documentation errors in section 2.1.2 when initially giving the depth_first_search example.

1) The example says "depth_first_search algorithm is a generic function accepting from one to four arguments by reference" but clearly the generic function takes 5 arguments with some by value.

2) The third argument listed in the prototype is given as "typename graph_traits<g>::vertex_descriptor root_vertex" but probably should be "typename graph_traits<graph>::vertex_descriptor root_vertex" as there is no 'g' argument in the prototype.

These are cosmetic documentation changes which should be made to allow someone who wants to understand the tutorial correctly to do so.