Rewritten furnaces

Furnaces now smelt the correct number of items.
Furnaces store their contents in a cItemGrid.
Furnace window is updated with correct items and progressbars.
Furnace recipes now use ticks instead of milliseconds.
Furnaces save and load their state completely, not missing a smelt operation.
Hoppers take items out of furnaces.
Dropped the cSlotAreaDropSpenser class, replaced it with generic cSlotAreaItemGrid

git-svn-id: http://mc-server.googlecode.com/svn/trunk@1601 0a769ca7-a7f5-676a-18bf-c427514a06d6