rt: fatal, 'chan->task == task' failed in upcall_del_chan

[robarnold]

Was trying to reproduce my mysterious double-free, found this instead. Single-threaded scheduler.
Testcase: https://gist.github.com/1082006

[eholk]

Thanks for catching this!

The problem is that we don't have move semantics working correctly for sends. I'm hoping to get this in there by the end of the week.