git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3293 c06c8d41-db1a-0410-9941-cceddc491573
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void reveal_secret_door(int x, int y)
{
ASSERT(grd[x][y] == DNGN_SECRET_DOOR);
dungeon_feature_type door = grid_secret_door_appearance(x, y);
grd[x][y] = grid_is_opaque(door) ?
DNGN_CLOSED_DOOR : DNGN_OPEN_DOOR;
}