Improved cursor behavior in regards to actors and FoW

This request should fix two issues I had with the cursor behavior:
1) When moving the mouse over a NPC, the cursor would change accordingly (to talk/attack), even though the NPC was hidden by the FoW
2) When moving the mouse near a NPC, but outside the circle, the cursor would appear as blocking, disregarding the underlying terrain.

I solved 1) by checking for visibility in GameControl.cpp and 2) by looking directly into SrchMap in Map.cpp, instead of calling GetBlocked (whose results are already pre-digested for the pathfinder)