adds windows/depends.py as a container for modules which are needed at runtime
but which py2exe's modulefinder dependency analysis fails to find as requisites.
there are many and various fiddly details that were involved in this process
on mountain view. This is a stripped down version of the build process used
there. there's hence a good chance that one or two necessary details got
stripped down through the cracks.
this provides a py2exe setup.py to build a tahoe.exe and a tahoesvc.exe
the former is equivalent to bin/tahoe, but without the start/stop commands.
the latter is a windows service that instantiates a client whose basedir
is found in the registry.
