Grid the landscape, and shortcircuit checks on the collision array if there are no nearby checked in collisions to be collided with. This is a big win for fire's ammoshove in particular. Also add a +2 that seemed missing in the check, and update fire accordingly.
[Desktop Entry]
Type=Application
Version=1.0
Encoding=UTF-8
Name=Hedgewars
GenericName=Fighting Hedgehogs
GenericName[tr]=Worms Benzeri Strateji Oyunu
GenericName[ru]=Битвы ежей
Icon=hedgewars.png
Exec=hedgewars
Terminal=false
StartupNotify=false
Categories=Application;Game;StrategyGame;