[Dbix-class] might_have support added, relationships refactored, happy birthday

[Andy Grundman]

Matt S Trout wrote:
> search_related
> create_related
> new_related
> find_or_create_related
> 
> to manipulate related classes and
> 
> set_from_related
> update_from_related
> 
> to manipulate ourselves when setting related objects.
> 
> I could really do with lots more tests for these - there're probably all
> sorts of lovely corner case bugs I haven't thought of.

I will work on some more tests. :)

-Andy