[Freeciv-Dev] (PR#7250) auto-settlers won't build mines over irrigation

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=7250 >

In the auto-settler code there's a check to see if there's already a 
conflicting improvement.  If so, no new improvement will be built.

But this is bad.  Say I transform my irrigated grassland into a hills. 
I want my settlers to build a mine on it.  The settlers should take into 
account the overall effect of the mining (-1 to food, +3 to shields) and 
count that against the cost of building the improvement.  I think this 
part is already done.

Changes are needed in ai_calc_irrigation and ai_calc_mine in 
server/settlers.c.

jason