Safe add node

[Nore]

I could be good to have a safe add_node function, which will do the same as add_node, but it the position is not loaded, save the change and do it after the map block is loaded.

[mauvebic]

Well usually when you hit an 'ignore' one of two things will happen: the block will wrongly replace a surrounding block, or if you have a later/earlier version with the fix in builtin/item.lua, the block won't place at all until the area is loaded.

[Nore]

I am mainly thinking to mapgen mods, for example landup, which will sometimes want to modify a node in a unloaded/ungenerated area, ignoring what is there, but for now it will not work.