prevent vehicle turrets from attacking their own car

[BevapDin]

Vehicle turrets use a fake npc to fire their gun. This PR adds checks for that fake creature and the vehicle they are on. It prevents calling map::shoot if this would damage the very same vehicle.

This prevents certain code that damages the terrain/furniture from being executed, but the squares should not have any of theses terrain/furnitures, because driving the car onto that square should have already damaged the content.

[KA101]

Uh, sorry, BevapDin. My armored car blew out its own headlight and steel plating shooting at soldier ants.

Screencap: https://www.dropbox.com/s/ifq0ub6tmp2v9yz/02072014TurretsStillSelfDamage.PNG
Save (immediately post-blowout): https://www.dropbox.com/s/wy0ke5sql98ydhb/Hustler.7z

[BevapDin]

Fixed it, was checking for (tx,tx) not (tx,ty) and my test case contained tx == ty, so the bug did not appear to me.

[KA101]

Np. This'll make a lot of vehicle-users very happy. When GlyphGryph gets back, remind me to put you in for four-star.

[HunterAlpha1]

going to try it out now.