Add support for running the test suite on another DB and/or schema

[ged]

Do you see any chance of making the tests run against a configurable database?

Well, getting the tests to run on a configurable database would be pretty easy: we could put the engine string into a small configuration file (or common python module). But testing for schema stuff is more complex than that I guess (I've never used schema so much): you'd need to pass the extra parameter to all table/entities... hmmm... or we might get away with simply adding the schema to the default table_options... That's probably a good idea.

I really think that should be doable because otherwise you might miss on bugs like the one I found, or not enforced constraints and the like.