Upspinfs on MacOS fails to copy file

[Rodrigo Schio]

When I try to copy a file from my local filesystem to upspin, using the mounted dir, it fails saying the file already exists, but that's not true.

```

Downloads$ cp ./Algorithms-JeffE.pdf ~/u/rodrig...@gmail.com/Public
cp: /Users/rschio/u/rodrig...@gmail.com/Public/Algorithms-JeffE.pdf: File exists

~$ ls -lh u/rodrig...@gmail.com/Public
total 1
-rwx------@ 1 rschio  staff     0B May  7 21:42 Algorithms-JeffE.pdf
-rwx------@ 1 rschio  staff    13B Jan 12 18:11 hello

```

The file appears on the directory but with zero bytes.

This problem doesn't occur when I use the upspin command.

E.g.: upspin cp ./Algorithms-JeffE.pdf rodrig...@gmail.com/Public