Display correct size of binary files in Diffusion

Test Plan: https://secure.phabricator.com/diffusion/P/browse/master/webroot/rsrc/image/header_logo.png

Reviewers: btrahan, epriestley

Reviewed By: btrahan

CC: aran, Korvin

Maniphest Tasks: T1139

Differential Revision: https://secure.phabricator.com/D3961