update JDBC driver loading to handle latest jdbc gems

latest gems no longer auto-load the driver jar but instead provide a `load_driver` method, this change is handled backward compatible (since not all driver gems are updated + users might decide to stick with an older gem version).

also maybe `HSQLDB` might get updated since there's now a **2.2.9** gem ... http://git.io/73rxYA
https://github.com/jruby/activerecord-jdbc-adapter/tree/jdbc-hsqldb-2.2.9/jdbc-hsqldb/lib