Fix "Show All Changes" button in Diffusion

Summary: See IRC. We currently render a "show all changes" button for commits which have more than 100 but fewer than 1000 changes, but it doesn't actually do anything. Make it do what it's supposed to.

Test Plan: Set the limit to 2; clicked the button.

Reviewers: chad, staticshock, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D6900