Build mkgmap/splitter #7

splitter_polygon_overlap_v1.patch : Improve splitting with polygonArea In some cases splitter wrote too much data into single tiles when options --polygon-file or --polygon-desc-file were used. The new algorithm checks a) rejects splits where a tile is has more than 50% of grid elements outside of the polygon and b) also considers the nodes outside of the polygon so that the output files are not too big for mkgmap