call getEntryInformation when possible
call getEntryInformation when possible

Summary:
When only directory entry information is needed, Eden offers a
fast-path lookup. Use it when only `name`, `exists`, and `dtype`
information is requested.

Reviewed By: wez

Differential Revision: D21291702

fbshipit-source-id: 3c8bdc9bfb9ca400762e7a400e728fcebcad1776

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