test preloading a HABTM association with hash conditions

It's related to #15244 
I had some HABTM associations using where in the definition, which were working on rails 4.0 and started to fail on rails 4.1. I though it was a bug, but I just realized they work if I add :table_name to where conditions.

So I have fixed that kind of association in test/models/project.rb and added a test for this case.