[mkgmap-dev] New, faster splitter

WanMil sent through a very nice patch for the splitter that writes out the results using multiple threads, giving a pretty big speedup during the 2nd half of the split if you have a multicore PC. For me, the time it takes to split the UK is less than half what it used to be. I've checked his patch in (r109) so feel free to give it a go. Note that by default the code will automatically use all available CPU cores but there's a new parameter --max-threads that you can use to control the number of cores that are used should you want to reduce them for whatever reason. Chris