Switch to side-by-side view

--- a/Allura/allura/templates/repo/diff.html
+++ b/Allura/allura/templates/repo/diff.html
@@ -1,5 +1,6 @@
 {% extends 'allura:templates/repo/repo_master.html' %}
 {% do g.register_forge_css('css/forge/hilite.css') %}
+{% do g.register_forge_css('css/forge/diff.css') %}
 
 {% block title %}
   {{c.project.name}} / {{c.app.config.options.mount_label}} / Diff of {{h.really_unicode(b.path())}}