Clean up vampiric_drain() a bit.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@5586 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on June 8, 2008
ZJ35GZK55U4IYTYDAVXTAMBNG5YF3LIGYD7OVTQH3UFA56I7JE5AC
Change contents