R1:21656f097198

Include only whole days in Differential stats

Summary: This prevents "8 active days" for last week.

Test Plan: `strtotime('1 week ago 24:00')`

Reviewers: john, epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D2794