This fixes all cases where the color profile was broken, and
libpng warns about. It also makes almost all textures indexed
instead of RGB where possible (textures that don't have
semi-transparent pixels).
To allow mapgen bushes in green-grass and savanna grasslands.
Nodes for a generic bush and an acacia bush.
Stem nodes are craftable to a single wood node to provide a small
amount of wood resource in grasslands.
Fuel times are that of corresponding 'wood' nodes, 1/4 that of
corresponding tree nodes.
No leafdecay to enable use as hedges or without a nearby tree trunk.
Uses 'default leaves simple' texture for extra visual thickness.
