In monsters::can_drown(), make monster vampires able to drown, as player

vampires can.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3620 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on March 13, 2008
BD5ZPI4AQYR4SHYGKH4FJ6XNNCGSSEXESF2HMD5WN4GJAJXAMGGAC
Change contents