Instead of returning 0 or 1, we'll now use ECMD_OK or ECMD_TURN.
These have the same meaning as the hardcoded numbers; ECMD_TURN
means the command uses a turn.
In future, could add eg. a flag denoting "user cancelled command"
or "command failed", and should clear eg. the cmdq.
Mostly this was simply replacing return values with the defines
in the extended commands, so hopefully I didn't break anything.
Pasi Kallinen
d53cd28d46