Prevent infected spawn immediately by human traps

[Socialdarwinist]

Right now it is possible to set infected spawn points outside of an infection zone, which is currently implemented for balancing reasons on infc_altepetl. Consequentially with this possibility, but also because of spawns on the edges of infection zones, there should be an other way than an infection zone to prevent spawnkilling. Either other spawns points shall be used or trap building there suppressed, of which the former is preferable because the latter is somewhat unexpected and contradictory to the player (he should be able to build his traps anywhere where he can tarry with impunity). It does no harm if the former is implemented with a protection radius of, say, one tee or tile around each spawn point.