Incorrect query when counting has n, :through relationships.

[postmodern]

I've reproduced a bug where dm-aggregates would not generate a GROUP BY clause to remove duplicate entries when counting a has n, :through relationship, thus resulting in inflated numbers.

git clone https://github.com/postmodern/dm-bug-report.git -b relationship_count
cd dm-bug-report/
bundle install
ruby bug.rb
DEBUG=true ruby bug.rb

[postmodern]

@dkubb is working on a patch for this (https://gist.github.com/67bb96fec0fbae59e505) and will likely be included in the 1.3.0 release.