Build mkgmap/splitter #22

- remove SparseLong2ShortMapHuge, - let SparseLong2ShortMapInline and SparseLong2IntMap use nearly the same code The code in SparseLong2ShortMapHuge was introduced to fix a problem with large input files which write a huge number of nodes into the same area. This happens e.g. with SRTM data or when you split planet with --num-tiles=2. The new code uses a better trick to circumvent this problem and thus has a smaller memory footprint.