Fix [2151183]: SIGHUP with the range view annotator active maintained

the annotated colours when saving. Fixed by adding the ability to store arbitrary exit hooks to be executed on (unusual) shutdown; for now they're executed FIFO, but it should probably be LIFO with a stack. Anyway the only thing that uses this now is the range view annotator. Oh, and it only works if you're using libunix.cc.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8999 c06c8d41-db1a-0410-9941-cceddc491573

Created by  haranp  on February 8, 2009
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