Honor schema in SQL query (Issue #931)

Or: Eating the same half of the pie twice

The issue was that even though the table expression has the correct schema the SQL generation was not using it.
The MappingQueryTests that you wrote yesterday now cover this case because they specify a schema which was previously ignored and is now included. This test is actually not really a query test, but an end-to-end test for creating a database with an arbitrary schema, saving into that database, and querying from it. I originally wrote it to use Migrations as well, but that doesn't work yet. I would like to leave it as a useful end-to-end regression test.