Revert "Boost performance of postgres specs by about 20-30%"
Revert "Boost performance of postgres specs by about 20-30%"

This reverts commit 4de935c31efbe6b3d2660cc3b327c86964c84c5a.

* DROP TABLE IF EXISTS is only available in > 8.2

datamapper/dm-core,alloy/dm-core,tpitale/dm-core,tillsc/dm-core,ar-dm/ardm-core,engineyard/dm-core