Foreign keys and SQLite

[jkuchar]

Version: master

Bug Description

I have been testing exception handling on PDO in #293 and I have found that SQLite does not check foreign keys by default.

Steps To Reproduce

Execute on test database (in tests/ directory)

INSERT INTO `orders` (`customer_id`, `product_id`, `amount`) VALUES (99999 /*non-existing*/, 1, 7)

Expected Behavior

Get ForeignKeyConstraintViolationException

Actual Behavior

It passes without exception

Possible Solution

Should be $connection->query('PRAGMA foreign_keys=true'); exucuted when SQLite connection is detected. Otherwise SQLite behave differently from other database backends.