fix Grease project reference ... must use GitHub project for GemStone 3.2

By itself we risk conflicts when loading Seaside3.1, so we will need to arrange to lock the Grease project for GemStone3.2. [For tODE, we've made a change to GsDevKit.](https://github.com/GsDevKit/gsDevKitHome/commit/d7c07bc3c5cc893b7dfdba926d58fa0e6c1ec51d)