Updated description of radioactive

Fixes #1412. Fixes #1421.

http://jenkins.buttonweavers.com:8080/job/buttonmen-blackshadowshade/522/
Suggested clarification: instead of "is involved in", say "is either the attacker or the defender in".

Regardless, i think this is an improvement and am happy to accept it --- just wanted to see if you like the idea of clarifying "involved" further.