Thanks to Mark Wielaard, the XRender pipeline has been merged with IcedTea6 [link].
The pipeline will be built by default, but disabled at runtime, to enable it simply pass -Dsun.java2d.xrender=True.
This way the pre-rewrite version can be used as driver-testing vehicle, hopefully it will lead to stable and fast drivers.
Small enhancements & bug-fixes:
I've just pushed a new version:
* Optimized line-rendering, not triggering fallbacks on GPUs without A8->A8 composition support.
This should be only relevant for i830 (everything smaller than intel-915 chipsets) as well as GeForce6/7.
* Fixed a bug which caused an unescessary mask copy at every non-solid operation (e.g. paints, or translucent colors). For some Java2Demo's this improved performance a *lot* :)
* I've fixed a bug Mark found, where I'd mixed up xrender and x11-pipeline initialization.