is_valid don't always revalidate the model. Added test also.
Tabel#create_joins can use through relationship and correctly join two table instead of one. Added through_key in configuration of HasMany
Add test for HasManyThrough and some small fix
HasManyThrough exploit definitions of the other relations and use the right keys. Test Done.
fix whitespace and coding style
add missing tables to pgsql fixture
resolve test errors
update naming of validated flag