Handle other pk types in PostgreSQL gracefully.

In #10410 it was noted that you can no longer create PK's with the
type of bigserial in PostgreSQL in 4.0.0.rc1. This is mostly
because the newer adapter is checking for column type with the
id column instead of just letting it pass through like it did
before.

Side effects:
You may just create a PK column of a type that you really don't
want to be your PK. As far as I can tell this was allowed in 3.2.X
and perhaps an exception should be raised if you try and do
something extremely dumb.
Test that #fresh_when accepts an array

https://github.com/rails/etagger/pull/3
Merge pull request #10455 from patricksrobertson/bigserial_id_not_identifying_pk

Add PK constraint on bigserial ID columns on postgres adapter
Revert "Merge pull request #10455 from patricksrobertson/bigserial_id_not_identifying_pk"

This reverts commit 3043d45eefc3776d5f3a9e7d212a01f99d869ef8, reversing
changes made to ca0275d36b395631725c4583db5a45c06443fdb9.