Add miscellaneous Enslave Soul fixes: make the mark last for 2 turns

instead of 1 at 0 Invocations, since the mark expires on the last turn, and fix inverted logic for determining when an enslaved soul should be twisted.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@10239 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on July 16, 2009
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