Various integration fixes

Fixed some integration tests that were causing Travis build failures and local build failures on a Windows box:
* Added sorting to columns before verifying to resolve issues where ordering can differ with different database versions
* Fixed issue where the stack for `ORMError` objects was undefined
* Fixed "done called multiple times" issue
* Fixed test that was failing for the redshift driver
* Fixed test that intermittently fails for sqlite due to race conditions with in-memory driver