A lot of instances where some function args are not actually modified in any way, meaning that it is better for performance to convert them into const references. This prevents an additional copy, which can help performance.
Pass a final boolean argument to TerrainBlock::import to control
y-axis flipping. It is enabled by default, since this was the previous
default behavior.
This should be added as an option in the terrain import dialog - see
game/tools/worldEditor/gui/guiTerrainImportGui.gui
