Adds on_throw_impact() so atoms can run special code when they hit things (hitby() handles damage still)
REMOVES GOOF CODE
gives the bikehorn a honk noise when it's thrown
makes the rubber ducky bikehorn not honk
removes POINTLESS comments from living_defense.dm
Fixes snowflake bikehorn code by adding it as a hitsound
Bikehorn now deals 1 damage, needed for hitsound (and it should atleast do SOME damage)
Merge pull request #654 from RemieRichards/30/05/2014-OnThrowImpact

Adds on_throw_impact() and assorted random changes