request for merge -- gc and numbers fixes

[email protected]/scm--integration--0.1 has a bunch of fixes for
numbers and gc along with a few tests copied from R5RS for numbers.
I'll add more as time continues.

I need to add a function for something like:

    scm_build_number (t_scm_word * result, t_scm_arena arena,
                      t_uchar * a, size_t len);

Any recommendations on the name or is build_number fine?

-jivera