Defective warehouses call after_dig_node which does not exist

[oversword]

All the defect variant of the warehouses do this:

	after_dig_node = function(pos, oldnode, oldmetadata, digger)
		wh.after_dig_node(Box, pos, oldnode, oldmetadata, digger)
	end,

wh.after_dig_node does not exist, causing a crash of you dig this node, worth looking back in the code to try and figure out why this is here in the first place.

I will probably get to it soon if you don't

[joe7575]

the wh.after_dig_node is missing since #51 and should be replaced with a wh.on_dig_node