Running "rb-site upgrade <path>" will fail if one of the media symlinks in <path> is broken. os.path.exists will say that the symlink doesn't exist, and then an exception will get thrown a few lines later when trying to create a symlink that already exists. This checks to see if dest_dir is broken symlink before doing anything, and if so, removes it.

Ran rb-site upgrade with valid and invalid symlinks.