Having trouble getting a build of Elixir 0.11.3 dev that works with the integration tests, just refactor the obvious problem ATM.

My old build lacked List.update_at/3, my latest grab through exenv throws ** (UndefinedFunctionError) undefined function: :elixir_quote.join/2.
Add Postgres integration tests for migrations.

For some reason, I always get #{n}_migration.exs:1: redefining module Ecto.MigrationTest.GoodMigration#{n} for any value of n when running the tests. This happens for integration_test/pg/migrations_test.exs lines 123, 110, and 109 in that order.