Set autoincrement and unique index fails

Maybe i'm wrong but setting a column like:
long("ordernumber").uniqueIndex().autoIncrement()

should be fine in case of Mysql. In newer versions its allowed to have a autoincrement column without the constraint of haveing it to be the primary key.

I got the following error:
```
org.jetbrains.exposed.exceptions.ExposedSQLException: java.sql.SQLSyntaxErrorException: Incorrect table definition; there can be only one auto column and it must be defined as a key
SQL: [CREATE TABLE IF NOT EXISTS good (id BINARY(16) PRIMARY KEY, active BOOLEAN NOT NULL, code VARCHAR(20) NOT NULL, description VARCHAR(255) NOT NULL, externalcode VARCHAR(30) NOT NULL, ordernumber BIGINT AUTO_INCREMENT NOT NULL)]
```

I not even see the unique Index there....

Using exposed : 0.32.1 with jdbc for mysql