Fix MONS_HELL_KNIGHT being considered an invalid monster class.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8239 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on January 5, 2009
GXSSXUSTSTLNSAI2GXBEAZ5JNTZWQ5F5R53WU7N2PY45XZS5NBKQC
Change contents