git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@1478 c06c8d41-db1a-0410-9941-cceddc491573
DKGRBWIZWKTE74OTWDMFVGOMHMU5LUNO5S5RMBOTEB2SFMFPFCWQC
UURAYLSSITZLQR56MCWFPIWMECU7F3USMA2UPJAO4IPIY5WVKP5QC
SW3RLYFNRT3IJBK6LYKHKP2J2YDU7SXQWAJZX7U6S7ICYW43OMNQC
K2CS6TCX2NDVL2ASEHGP4J4K4IJ6FP3ANNKTSIWVG43HPYSBX6ZQC
ASSERT(env.cgrid[i][j] == EMPTY_CLOUD);
env.cgrid[i][j] = EMPTY_CLOUD;