Fix errno includes, and hopefully DOS compile [2573206].

If errno.h doesn't exist on DOS, this will fail, but then it would have failed anyway.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8978 c06c8d41-db1a-0410-9941-cceddc491573

Created by  haranp  on February 8, 2009
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