add __repr__ to CallFromThreadObserver

darcs-hash:20090225160033-b2873-34bf1fce2d92f7f5c30ce1f000eb74a96f145a2e
fix GreenEngine.linked_incoming

darcs-hash:20090225160156-b2873-ed57d5e6ded934012161c4343d48671a81707925