[mkgmap-dev] Fix Sea Patch

Hi Gerd, Mkgmap used to contain some code that attempted to correct incorrect sea and land data where polygons were ordered in the wrong direction. This was removed some time ago because it didn't work properly. I have put together the attached patch that works much better and have been using it for some time. With the sea data that I use, which contains quite a large number of incorrectly ordered polygons, it manages to correct every error it finds. It won't be able to fix really gross errors, but providing most of the data is correct it will produce good results. Please review and commit if happy. Cheers, Mike