By eliminating the linear look up of the dirtyQueue for every newly added rendering request, it should be possible
to significantly increase the length of the dirty rendering queue. At the moment the queue length is set to 1000 metatiles,
which at a typical rate of 2 - 3 metatiles a seconds is a buffer of only 5 - 10 minutes. With a much longer
queue, the excess daytime requests can be moved into the quieter night time hours, which could improve the overall long-term
throughput if the server is at its limit of what it can handle.
All operations on the dirty queue should now be O(1).
Made renderd more configurable at runtime: socketname, num_threads and the mapnik settings plugins_dir, font_dir, and font_dir_recurse are now available through renderd.conf
There should be only one incompatible change: the [Default] section in the config is now in all lowercase "[default]" because the parser lib gives section and key names back in lowercase
