* I didn't understand that expression last fix and now the furnace would burn fuel
even when it had no source item.

This one contains these changes from main c55:
* Adds a function to check if there is room for a specific item
* Using that, you can now pick up rats if you have a full inventory and a not full rat stack
* Furnace would cook only 1 item if that item used the last available result slot, now it will continue
* Furnace will say it's overloaded
* Furnace won't wait until the next step to start on the next item
 - This caused small fuels to cook slower than meant to
 - Also caused furnaces to say they were out of fuel after finishing the last fuel item

Moved some mapnode content stuff from mapnode.{h,cpp} and digging property stuff from material.cpp to content_mapnode.{h,cpp}

Reduced server CPU usage on NodeMetadata step()s. Also furnace now cooks while no players are near it.

--HG--
rename : data/tool_stpick.png => data/tool_stonepick.png
rename : data/tool_wpick.png => data/tool_woodpick.png