Prevent logging ENOSYS errors for ReleaseFileHandle.
Prevent logging ENOSYS errors for ReleaseFileHandle.

Fixes #76.

mbrukman/gcsfuse,BanzaiMan/gcsfuse,jacobsa/ratelimit,kahing/gcsfuse,GoogleCloudPlatform/gcsfuse,GoogleCloudPlatform/gcsfuse,GoogleCloudPlatform/gcsfuse,BanzaiMan/gcsfuse