Allow MySql in UnitTests

At the moment it is impossible to follow our normal development guidelines when implementing database-dependent code as the behaviour of the code in MySql cannot be unit tested.
We should make it possible to the unit tester suite
simply by specifying the mysql connection information in settings.xml or
as command-line properties. At the moment this will not work because (among other
things) DatamodelTestCase is derby-specific. It should be possible to make this class detect the db type and modify its behaviour accordingly. The jdbc mysql
connector would need to be added to tests/lib and test.policy would also need to have the right permissions. I would estimate 2md.
[Alternatively: move the entire persistence layer to Hibernate. All DAOs would need to be reimplemented (CRUD methods can be done polymorphically). We
would then transparently support all major rdbms flavours.]