Change Options.autopickup_on from boolean to 3-state: 1 (autopick up), 0

(autopickup off), -1 (autopickup turned off automatically). Only in the latter case does killing an invisible monster turn autopickup (back) on.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@9691 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on April 24, 2009
HP72STXEK6KJ5SAPZKKLLAXC5HB7J4E6X6NK2BNFP6GARF52K5RQC
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