R1:3dd12e7cc6e7

Changed 'diffusion.getrecentcommitsbypath' to return only the direct and child
changes.

Summary:
It was incorrectly returning copies.

Test Plan:
Tested that the conduit call for 'tfb/trunk/www/last_min_rev.txt' matches
https://phabricator.fb.com/diffusion/E/history/tfb/trunk/www/last_min_rev.txt

Reviewed By: jungejason
Reviewers: jungejason, epriestley, aran
CC: aran, jungejason
Differential Revision: 340