Issue #3025: string -> boolean for profile_background_tile entry in JSON user results from Twitter-compat API

This entry was using the strings 'true' and 'false' instead of literal booleans, which could confuse clients expecting literal booleans as in other places and on Twitter in this place.

lib/apiaction.php

@@ -263,8 +263,7 @@ class ApiAction extends Action
             ? Design::url($design->backgroundimage) : '';
 
         $twitter_user['profile_background_tile']
-            = empty($design->disposition)
-            ? '' : ($design->disposition & BACKGROUND_TILE) ? 'true' : 'false';
+            = (bool)($design->disposition & BACKGROUND_TILE);
 
         $twitter_user['statuses_count'] = $profile->noticeCount();