* Move check from generated helper to test_help.rb, so that all
applications can benefit
* Rather than just raising when the test schema has pending migrations,
try to load in the schema and only raise if there are pending
* Opt out of the check by setting
config.active_record.maintain_test_schema = false
* Deprecate db:test:* tasks. The test helper is now fully responsible
for maintaining the test schema, so we don't need rake tasks for this.
This is also a speed improvement since we're no longer reloading the
test database on every call to "rake test".