Clean up explosion routines a bit more, and put back erroneously removed

Tome of Destruction explosion.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8533 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on January 17, 2009
6G55KX5P4X7RFJAOJ7QU4ATMWC3ZVTCXKVHTYEAH5JYYGZCFQ7SAC
Change contents