Boxes And Trails update! This also adds more 'not ground' blocks to the find-ground routine, and refactors it.
Fence Gates create fences (though LinkedTrail doesn't really link them as a rule). Boat creates rivers: water blocks along the path of flight. I don't yet have it transforming the very messy result into smooth pools of water, but it avoids making water-mountains. There's a removed reference to Water Lily, which will need its own routine as it places a linked trail only on Stationary Water blocks. And, BoxSnowball is created. It works with leaves, and Empty Bucket, and responds to power. It makes a big cube of the material, hollow, with the inside free of liquid. The leaves are NOT player placed, and will decay, which is a neat gotcha for those making bridges out of Leaf Boxes. Have not yet decided what other solid blocks can become Box, but it makes lovely huge boxes when double glowstoned.