This reverts commit fe985960, reversing
changes made to add95606.

test identity map and not fully removed when the feature was removed.

Dear Active Resource,

It's not that I hate you or anything, but you didn't get much attention lately. There're so many alternatives out there, and I think people have made their choice to use them than you. I think it's time for you to have a big rest, peacefully in this Git repository.

I will miss you,

@sikachu.

Don't install ruby-debug if running the test suite on Travis,
linecache19 is the main offender, very very slow.

And do not install pg if Travis is bundling the gems, pg will be setup
on Travis soon.