Tweak some descriptions.

Also: Some of the abilities don't have any descriptions yet, so if anyone has an idea, please add some. (Even bland one-liners are better than "has no description yet" but I've run out of ideas and am not even sure what most of the remaining ones do.)

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6404 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on July 5, 2008
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