Downgraded Database_cleaner gem from 1.0.1 to 0.9.1 and locked version dependency to 0.9.1 in Gemfile.

It seems 1.0.1 was broken, or at least acceptance tests were failing with it. 0.9.1 seems to work fine. Will investigate it if I have time but for now I will use the last known good version, 0.9.1, and be done with it.