Simplified 'Upstream using symlinking'

These changes approach several issues:

 1. A directory name ending with '.git' is normally a bare repository. But we need a checked out repository here. So I replaced it with '.dev' to avoid a collision with the normal install procedure (cloning to git-ftp).
 2. The subdirectory 'develop' makes the script more complex without benefit in this scope.
 3. Removed unnecessary `cd` commands.
 4. Added update for Windows install as requested by #114.