aeson 0.7 support for persistent #197

Note that persistent-mongoDB and persistent-redis do not compile.
Revert "persistent-postgresql: Produce correct alter table statements for non-primary foreign references"

Relevant to issue #196

This reverts commit a737f484b3d86430ccba9e399740e7bc40e09e11.

Conflicts:

	persistent-postgresql/Database/Persist/Postgresql.hs
add a test for repeated migration