Another progress report

The dynamic caching is working on everything but the sea-flooding. I have successfully made a 32,768 x 32,768 heightfield. It took 10 hours on an AMD XP2600, and only took 25Mb of RAM (though ~5Gb of HDD). The dynamic caching routines are about twice as slow as the RAM-only operations, but I think I can optimise a few things there.

ETA for release 2.1 is at least two weeks from now.