rails 4: only load pg types we care about
rails 4: only load pg types we care about

in massively sharded databases where there's a type for every table,
this reduces the number of rows queried and unused... massively

Change-Id: Ib9bcf70d060f5ba48ebedaa7108d9d364430c638
Reviewed-on: https://gerrit.instructure.com/61975
Tested-by: Jenkins
Reviewed-by: Brian Palmer <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

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