Fixed a ReadDir -> ReadDirAll regression.
Fixed a ReadDir -> ReadDirAll regression.

Added static assertions to make sure it doesn't happen again.

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