Sync with zs. - Fix some bogosity with mixing unit numbers and channels, which would only   work for one instance of the device. - Use a simpler scheme for input and output queueing. - Use db_alt_break.
Sync with zs.
- Fix some bogosity with mixing unit numbers and channels, which would only
  work for one instance of the device.
- Use a simpler scheme for input and output queueing.
- Use db_alt_break.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase