[New Feature] Allow pure AA occupants to actually fire at aircraft.

[maistral]

Description:

Allow occupant infantry to fire at aircraft. As it is now, to actually fire at aircraft, infantry occupying buildings need to have BOTH AG=yes and AA=yes set. If you attempt to set AG=no and leave AA=yes set, the said infantry won't fire at any aircraft.

IE: since GGI's launcher can have both AA=yes and AG=yes it can fire at aircraft while hiding in a building. However, Flak Trooper with only AA=yes and AG=no (using the anti-air flak cannon) disallows this to happen.