symlink in the sync tree causes an error

[oconnor663]

Traceback (most recent call last):
  File "/usr/bin/peru", line 11, in <module>
    load_entry_point('peru==1.1.2', 'console_scripts', 'peru')()
  File "/usr/lib/python3.6/site-packages/peru/main.py", line 371, in main
    run_task(command_fn(params))
  File "/usr/lib/python3.6/site-packages/peru/async_helpers.py", line 29, in run_task
    return asyncio.get_event_loop().run_until_complete(coro)
  File "/usr/lib/python3.6/asyncio/base_events.py", line 467, in run_until_complete
    return future.result()
  File "/usr/lib/python3.6/site-packages/peru/main.py", line 94, in do_sync
    params.runtime, params.scope, params.imports, params.runtime.sync_dir)
  File "/usr/lib/python3.6/site-packages/peru/imports.py", line 18, in checkout
    previous_index_file=index)
  File "/usr/lib/python3.6/site-packages/peru/cache.py", line 426, in export_tree
    yield from session.checkout_files_from_index()
  File "/usr/lib/python3.6/site-packages/peru/cache.py", line 190, in checkout_files_from_index
    yield from self.git('checkout-index', '--all')
  File "/usr/lib/python3.6/site-packages/peru/cache.py", line 78, in git
    raise GitError(command, process.returncode, stdout, stderr)
peru.cache.GitError: git command "['git', '--git-dir=/home/jacko/.peru-cache/trees', '--work-tree=/home/jacko/dotfiles', 'checkout-index', '--all']" returned error code 128.
stdout: 
stderr: fatal: cannot create directory at 'vim/bundle/fzf': File exists

After manually replacing the vim/bundle/fzf folder with a symlink to different repo, and then running peru sync. I expected a "dirty repo" error instead.