[Tilecache] TileCache-2.0ish refactor

[Christopher Schmidt]

I just pushed through a major refactor in TileCache SVN.

My *hope* is that this refactor is unlikely to break any existing
applications, with the exception of users using the Memcached cache:
that cache has now changed to be called the "Memcached" cache.

This is the result of work I originally did in the 'refactor' branch
around the time of 1.9's first RC. The big difference here is that
TileCache Layers, Caches, and Services are all seperated out into
seperate files, making it much simpler to extend TileCache with your own
Layer types and the like. 

A request a couple weeks ago from Graham Carlyle
(http://openlayers.org/pipermail/tilecache/2007-November/000575.html)
has been integrated into this design: Graham, this means you can
probably use trunk of TileCache now without changing anything on your
setup. (There is a way in the tilecache config to ad paths to your
sys.path if that's neccesary for you.) 

Splitting these things up allows TileCache to be more modular, and means
that the types of layers can be extended more easily.  

The new branch also includes:
 * A basic ArcXML Layer
 * A first stab at a KML superoverlay support (which I'm not really
   particularly sure of, but it does do something in GE)
 * Fix to a problem where having /etc/tilecache.cfg on your system
   would override all TileCache configs under CGI

I know this is somewhat abrupt, but I don't have a lot of time for
TileCache at the moment, so I wanted to get everything back to trunk
before I forked too far to do it again. With the exception of the
memcached layer changing name from MemoryCache to Memcached, I think
that everything will continue to work exactly the same by default. Bug
reports welcome on that front -- though since this is my target for 2.0,
I'm likely to only add them to a migration doc, rather than fixing them,
if they come up.

If you have a development environment, and can test the new TileCache
code, I'd appreciate it: please don't treat it as production ready yet.

Regards,
-- 
Christopher Schmidt
MetaCarta