git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6946 c06c8d41-db1a-0410-9941-cceddc491573
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AZ2RCXNVULJUSCBDBK3VARTUCTPEJXHTA7ALP73S4EXLJB6YYB5QC
K2CS6TCX2NDVL2ASEHGP4J4K4IJ6FP3ANNKTSIWVG43HPYSBX6ZQC
MDAJYB6STTZPNHRQ2X66MMMSONMKXTESLHJSFPGN7H3D3TOVBAVAC
ac_change = arm.plus;
ac_change = property(arm, PARM_AC);
ac_change = arm.plus - ac_change;
ac_change = property(arm, PARM_AC) - ac_change;