K-Mod pathfinder

[joseasoler]

K-Mod includes a pathfinder which is supposed to improve efficiency and memory consuption a lot. As it seems to be a very isolated component (which can be enabled or not by using the KMOD_PATH_FINDER compilation flag), its inclusion should be considered. See https://github.com/karadoc/Civ4-K-Mod/commit/5f7bda705edd5a5d480cb23acb6b51e9836d5613