Comment 9 for bug 1211276

After discussing this with Randall, I think we can omit the "ORPHANED" status. So it'll be:

- API sends action to engine (round-robin)
- Engine checks status of stack
- IF stack status == "INPROGRESS":
  + Broadcast "Stop working on stack X" message to all engines
  + Wait for response (0.5 sec timeout)
- Proceed with operation