Fixes #9.

This manifested as ForgetFSTest.MkDir pacicking now and then in a manner
like this:

    https://gist.githubusercontent.com/jacobsa/2d12150beca1043f71b0/raw/28e0a01a9276799ad820970a05b522367222c331/gistfile1.txt

For #9.

See bazil/fuse#89 for more details.

Caused by jacobsa/bazilfuse@47700022b94da7c946b1f5f8af8621b2a32f4762.

For #9.

Now that I have some references to cite.

For GoogleCloudPlatform/gcsfuse#60.