Unclaimed task return values pollute NS

[svoboda]

In a problem similar to UNIX zombies, when a task spawns another task and does not claim its return value with task_wait(), the record containing the return value will linger in NS. This can lead to NS consuming more and more memory, while it is not NS which is at fault.

[svoboda]

For better resource accounting, the interface should be changed such that the result is always either delivered to the parent task or discarded. Should the parent task forget to dispose of the return values, its own memory footprint will increase. This makes it easier to pinpoint the leak or possibly even kill the offending task.