Diffusion - return 404 errors for bad URIs

Summary: Fixes T5646. Makes diffusion a much better user experience. Users now see a 404 exception page when they have a bad URI. Previously, they saw a developer-facing raw exception.

Test Plan: played around in diffusion a bunch. most of these changes were fairly mechanical at the end of the day.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T5646

Differential Revision: https://secure.phabricator.com/D11299

src/applications/diffusion/controller/DiffusionChangeController.php

@@ -6,9 +6,9 @@ final class DiffusionChangeController extends DiffusionController {
     return true;
   }
 
-  public function processRequest() {
+  protected function processDiffusionRequest(AphrontRequest $request) {
     $drequest = $this->diffusionRequest;
-    $viewer = $this->getRequest()->getUser();
+    $viewer = $request->getUser();
 
     $content = array();
 
@@ -62,7 +62,7 @@ final class DiffusionChangeController extends DiffusionController {
     $changeset_view->setRenderURI('/diffusion/'.$callsign.'/diff/');
     $changeset_view->setWhitespace(
       DifferentialChangesetParser::WHITESPACE_SHOW_ALL);
-    $changeset_view->setUser($this->getRequest()->getUser());
+    $changeset_view->setUser($viewer);
 
     // TODO: This is pretty awkward, unify the CSS between Diffusion and
     // Differential better.