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This is a hack to fix lighting and fluid transform issues automatically,
using a carefully metered allotment of CPU time to do background
recalculations.

At the time of this mod's creation, minetest still has a lot of issues
with lighting and fluid flow, especially when recalculating these things
near the loaded/ignore frontier, and in map generation.

Some example issues:
	- Mapgen lighting seems to look only at the heightmap, and
	  ignore other changes, such as adding water or trees, so e.g.
	  the ocean floor will be incorrectly fully-lit.  Custom mapgen
	  cannot seem to modify the heightmap, so large carve-outs may
	  end up unlit.
	- Large multi-node operations, such as tree growth or schematic
	  placement, may create large shadowed areas.
	- Fluids may still not flow properly into caves in some places.

This mod addresses these by:
	- Doing an extra fluid/lighting calc on each actual mapblock
	  soon after map generation, to fix at-generation issues.
	- Doing random background recalcs on mapblocks near players
	  continuously as the game runs.

See init.lua for configuration options.  Settings are set to sane
defaults for a server that is NOT heavily loaded; some tuning may be
necessary otherwise.

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