Implemented DirInode.ReadEntries.
Implemented DirInode.ReadEntries.

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