documentation: small errors in the tutorial

[Harald . Korneliussen]

Hi, I found some small errors when trying out the excellent tutorial at

http://www.gnu.org/software/guile/docs/guile-tut/tutorial.html

The tutorial makes use of a function SCM_NUM2DBL to transform an SCM num
thingie into a double. But when it compiles it can't find that function.
>From reading the documentation I believe the correct function is
gh_scm2double.
When I replaced SCM_NUM2DBL with gh_scm2double it compiled correctly and
performed as expected.

Also, there is a small issue in the following test

{
    int ii;
        tortoise_pendown();
        for (ii=0; ii<4; ii++) {
            tortoise_move(100);
            tortoise_turn(90.0); /* Here: it takes an int as an argument */
        }
        /* sleep for a bit so the window stays visible */
        sleep(10);
}

It should really be 90, not 90.0. When you (like me ;-) forget to make
proper prototypes 90.0 and 90 are not the same... another of C's little
suprises :-D You might correct that while you're at it.

Thank you for your time, and for the nice documentation