halted waiting robots are stuck in limbo and cannot be reprogrammed

[byorgey]

Describe the bug
If a robot is waiting and is killed via halt, it seems to get stuck in a state where its CESK machine is Up, waiting to propagate an exception up to the top level to cancel its running process, but it never gets a chance to run since it is waiting. This means, for example, that it cannot be reprogrammed or salvaged, since the system still considers it to be actively running a program.

To Reproduce
In creative mode:

> r <- build {move; wait 1024}
> halt r
> reprogram r {selfdestruct}

This should work and result in the built robot disappearing. Instead, we get an error about not being able to reprogram a running robot. However, if you wait the 1024 ticks and then try reprogram again, it works.

For comparison, if we replace the wait with a busy loop then it works fine:

> def forever = \c. c; forever c end
> r <- build {move; forever (turn left)}
> halt r
> reprogram r {selfdestruct}

Expected behavior
Calling halt on a robot should move it out of the "waiting" state so it can immediately do finalization/cleanup and transition to an idle state.