Windows symlink dereference (so old servers can be deleted)

Dereferencing a symlink on Windows is difficult and I couldn't find a working Python solution. This adds an auxiliary text file alongside the symlink on Windows that contains the target directory name, and also heuristics for testing whether a symlink and a directory are the same (https://github.com/manics/omego/commit/80c1b0079b07690feb0d5e8d643064df062ee629).

Will be tested on Hake once release testing is done.