[Tilecache] Controlling the tile IDs

[Martijn van Oosterhout]

I'm trying to make two tile services with different bounding boxes
line up, and it's not working very well. So I had an idea about how to
make it easier. It involves adding two options: origin and
invertYaxis. And then we change the tile calculation to work off the
basis of the origin, inverting the Y axis simply replaces Y with -Y.
The default origin would be the lower-left corner. As a side-effect it
can also handle the google TMS type by setting the default origin to
the upper-left and setting invertYaxis to true.

This would make it trivial to make different layers line up. What do
people think?

Have a nice day,
-- 
Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/