Update the changes log with all the changes up to this point.
Overhaul isa_ok() and fix it for perl 5.17.

5.17 (and thus 5.18) changes how '#!%@#$!blah'->isa is resolved.  Now
any string will be treated as a class name.  See rt.perl.org #105922

This required changes to the isa_ok() and I decided to overhaul
the logic so it's more organized.  I also changed the formatting,
hopefully more sensibly.

For #353
Update the change log.
Require Scalar::Util used by isa_ok()

1.13 is the version which shipped with 5.8.1.

Don't make 5.8.1 the minimum Perl to allow it to still work on 5.6
if they have Scalar::Util.