backport SchemaCreation (from AR 4.0/master) for MySQL
review Postgres' SchemaCreation to match our convention
setup 'bare' SchemaCreation for Derby + less garbage noise from `distict`
hook-up SchemaCreation for HSQLDB/H2
re-invent `add_column_options!` (due next AR 4.1) to provide compatibilty
Oracle, MS-SQL and DB2 adapters still need it as they are not refactored to the knew "AREL-style" `SchemaCreation`, this will make sure they work with 4.1
AR's `distinct` compatible with 4.x (and 3.x) for Oracle, Derby and Postgres