Explicitly set :limit on all DB migrations adding string columns
Rails 4.2 changes the default options for string columns in DB migrations, removing the default limit of 255 characters for PostgreSQL and SQLite adapters (it remains for MySQL, since that's the limit of a VARCHAR).
All of our existing DB migrations should be changed to set
:limit => 255 on add_column .. :string calls if no limit is already set. This will ensure that a database created on earlier versions will be exactly the same as one created on Rails 4.2.
I don't think we should change the limits of any columns while doing this, just be explicit about what limit they currently have. If we want to change limits, that should be done as an additional DB migration so the behaviour across versions is consistent.