Made the flipped y-axis on terrain import optional.

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

Engine/source/terrain/terrData.h

@@ -233,7 +233,8 @@ public:
                   F32 heightScale, 
                   F32 metersPerPixel,
                   const Vector<U8> &layerMap, 
-                  const Vector<String> &materials );
+                  const Vector<String> &materials,
+                  bool flipYAxis = true );
 
 #ifdef TORQUE_TOOLS
    bool exportHeightMap( const UTF8 *filePath, const String &format ) const;