Turns out we could conquer a village and then settle a new one without
having enough expansion slots. Thus this is a revert to original state,
where we can't train settlers with chieftain in village or chieftain
with settlers in village, if we don't have enough slots.
Closes#324
It is debatable whether or not to allow this, since chieftan would be of
no use once we have 3 settlers and settle a new village. However, if we
accidentally created a chieftan, we can't train settlers until we send
the chieftan to his death.
I think this move could be a predule to a later game mechanics, where
chieftan could fight (talk, actually) against chieftan, if one is
present in village, so taking a village over isn't so easy.
Martin Ambrus