never return timestamps for clock fields on eden file results
never return timestamps for clock fields on eden file results

Summary:
Eden mounts don't support timestamp queries, and the cclock and oclock
fields only include the tick value. To avoid the "new" field resolver
from fetching full stat information, don't populate the timestamp
fields at all.

Tangentially, I believe we could deprecate timestamp queries entirely,
requiring that Watchman users use clock values. This would mean we
could remove the timestamp field from the clock struct entirely.

Reviewed By: wez

Differential Revision: D21291252

fbshipit-source-id: 1550f5fadf1740ed1ddc520a29515841e69efffe

nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman