[Freeciv-Dev] (PR#6112) Civ3: Reforest tech

["Marko Lindqvist" <marko.lindqvist@xxxxxxxxxxx>]

  Please note that civ3 compatibility is not freeciv goal. We might 
decide that this feature is not to be included into freeciv.

  In civ3, engineers can reforest only after Engineering is discovered.

  Other games (SMAC, CTP2) have similar limitations. One can 
irrigate/mine certain terrain types only after related technology is 
discoverd. So this is not required for civ3 ruleset only, but for 
several rulesets.

  Probably cleanest way to implement this is to add fields 
'irrigation_tech' and 'mining_tech' to each terrain type at 
terrain.ruleset. This could also be implemented using req_gen framework.


  - Caz