Sorry to bump this old topic, but I propose making a change to the wikipedia article here.https://en.bitcoin.it/wiki/Contracts#Example_5:_Trading_across_chains
"Currencies that implement the same ideas as Bitcoin can be traded freely against each other without trust."
This statement is false. As Sergio has described, the GMAX/luxgladius scheme is inherently insecure because it either a) has no timeout, in which case funds could be locked up forever, or else it b) relies on timeouts in the two chains which leads to a race condition where one guy could run away with the funds.
The P2PTradeX solution he describes would require substantial hard-fork changes to Bitcoin - essentially, you would have to be able to encode the validation rules for the altchain in a transaction script.
So, my suggestion is to remove the GMAX/luxgladius example from the wiki and explain that it currently thought to be impossible to trade between altchains and bitcoin without trust, and include a link to this thread.