fix Default scope, use table connection for generating sql

[fmnoise]

We found and issue, when acts_as_paranoid is used with database_cleaner gem and multiple database adapters like mysql and postgresql. We had the following errors

Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '."deleted_at" IS NULL) LIMIT 1' at line 1: SELECT users.* FROM users WHERE users.id = 42 AND ("users"."deleted_at" IS NULL) LIMIT 1

[zzak]

Needs a rebase

[zzak]

@fmnoise Thank you!