Table engine support

[JanJakes]

Currently, the SQLite driver saves the specified table engine in the information schema, but it doesn't emulate different engine behavior in any way, nor it checks whether the engine is supported. At the moment, we expect the engine to be InnoDB.

WordPress also works with MyISAM, and there are other table engines in MySQL.

We probably could implement support for some additional engines (ignore FKs for MyISAM, etc.), but until then, we can trigger a warning when an engine other than InnoDB is used.

Additionally, we should make the warnings configurable:

These warnings will quickly get annoying so we could add a driver-level warning control with an option such as "warnings" => array( "db_engine" => true|false, ... )

See also: Automattic/sqlite-database-integration#21 (comment)