Modified to implement postgres adapter and...

...postgres sql changes

567 examples, 0 failures
Coverage report generated for RSpec to /Users/yzhang/the_policy_machine/coverage. 624 / 702 LOC (88.89%) covered.
Passes with mysql and postgres backends
Passes specs in dalton postgres branch with this commit on postgres, mysql and memory backends
nitpick: Should probably `s/mysql/postgres/g` in this file just to avoid confusion later (especially if we end up connecting to both dbs in parallel for faster tests).