[crossfire] Circular lighting & negetive glow_radiuses

[Mark Wedel]

  Some notes about the patch:

General: Never use // comment style.

common/living.c: Making the glow radius additive is probably a bad thing.  A 
player shouldn't be able to light a few torches and get an effect to see 
everything about them (plus in real life, given the (pi)r³ of real lighting, 
doesn't much up very well.).  Same note applies for map.c and server/spell_attack.c

common/object.c: op->glow_radius !=0 would be clearer checks that >0 and <0

server/monster.c: while seeing how well lighted the creatuer is may make sense, 
until we do something with that, I'd much rather just return once we know if the 
creatuer is illuminated or not for performance reason - checking for all the 
spaces for all the monsters could prove to be a pretty big cpu hog.