Supporting multiple backends requires that specific sqlite
collations are not used, thus lowercase is applied to all non
case-sensitive columns. However, lowercasing the database requires
temporary disabling foreign key constraints, which is not possible
on SQLite and requires we specify the constraint names.
This migration specific to sqlite and postgresql drops every
constraint, whether it is named or not, and recreates all of them
with known names so we can later disable them.
kaiyou