If a node is specially tagges with the stack_as_node group, and
the stack size is exactly 1, place as a real node instead of a
stack node.
This reinstates logic from WAY back in the super-early pre-alpha
days, except only for nodes explicitly tagged this way.
This should be applied only to nodes that aren't transformed in
any non-desirable way when placed as nodes instead of stacks, and
can be dug the same ways as stacks (i.e. snappy = 1 or
crumbly = 1).
Currently applied to sticks, staves, leaves, ladders/frames,
and torches. Ladder/frame placement offers some interesting
possibilities in terms of throwing ladders to rappel down holes.
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