Correct - we do have a slip-up with the latest release in terms of the build instructions. As the Incubator Project has evolved we have created a more elaborate build infrastructure internally to support more advanced testing and build tooling, and that is what you are seeing in terms of the import reference. For now, I suggest that you just ignore the build.xml in there and create one of your own.
We will post back here when we have an updated instruction on how to build.
Thanks for letting us know. Sorry for the confusion.
Good news is that we're in the process of re-packaging the Incubator distribution, including source code and examples, into a form that will make all of this easy.
The plan is to release this as Incubator 10 (Patch 5). It's been a little delayed due to ensuring Patch 4 was released (which occurred yesterday).
We're starting on Patch 5 next week.