Fix spell power caps not being respected (looks like a long-standing bug.)

Code quality improvements for Twist.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8358 c06c8d41-db1a-0410-9941-cceddc491573

Created by  haranp  on January 9, 2009
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