[mkgmap-dev] Include the following patches into trunk -- Patch4 - decrease douglas peucker error

This is the last patch for the series. I'm not really sure if it should be applied. I don't even find out where I got this patch from. I just assumed that someone thought about writing it, and hence it provides some benefit. I really don't know whether this patch improves or degrades the map. Actually mostly wondering on what it is worth: