Slight cleanup of randart autoinscription.

Code cleanup with unrandarts and fixedarts. Bugfix for isomorphic-up-to-colour unrandarts being confused when lost in the Abyss. Trowel will not clobber critical features (stairs, portals, etc.) Nemelex is unhappy about Trowel failing. Breaks savefiles.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3003 c06c8d41-db1a-0410-9941-cceddc491573

Created by  haranp  on December 5, 2007
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