GeoAlchemy 0.7.1 doesn't work with SQLAlchemy 0.8.0b2

This has been [reported](https://groups.google.com/forum/#!topic/geoalchemy/vSAlsuhwWfo/discussion) on the mailing list. A [fix](https://gist.github.com/4497133) was found by @zzzeek and I on [Twitter](https://twitter.com/erilem/status/289122470433275904).