Fix logged-out Diffusion calls to Conduit

Summary:
Conduit doesn't currently have an analog to "shouldAllowPublic", so the recent policy checks added here caught legitimate Conduit calls when viewing Diffusion as a logged-out user.

Add `shouldAllowPublic()` and set it for all the Diffusion queries.

(More calls probably need this, but we can add it when we hit them.)

Test Plan: Looked at Diffusion as a logged-out user with public access enabled.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7380

src/applications/diffusion/conduit/ConduitAPI_diffusion_abstractquery_Method.php

@@ -6,9 +6,14 @@
 abstract class ConduitAPI_diffusion_abstractquery_Method
   extends ConduitAPI_diffusion_Method {
 
+  public function shouldAllowPublic() {
+    return true;
+  }
+
   public function getMethodStatus() {
     return self::METHOD_STATUS_UNSTABLE;
   }
+
   public function getMethodStatusDescription() {
     return pht(
       'See T2784 - migrating diffusion working copy calls to conduit methods. '.