Replace deprecated trigger_error calls with exceptions

controllers/EditTag.php

@@ -39,13 +39,13 @@ class EditTag extends HTMLController
 				exit;
 			}
 			else
-				trigger_error('Cannot delete tag: an error occured while processing the request.', E_USER_ERROR);
+				throw new Exception('Cannot delete tag: an error occured while processing the request.');
 		}
 		// Editing one, then, surely.
 		else
 		{
 			if ($tag->kind === 'Album')
-				trigger_error('Cannot edit tag: is actually an album.', E_USER_ERROR);
+				throw new Exception('Cannot edit tag: is actually an album.');
 
 			parent::__construct('Edit tag \'' . $tag->tag . '\'');
 			$form_title = 'Edit tag \'' . $tag->tag . '\'';