Allow mode='rt' on open_resource() helper

flask/helpers.py

@@ -1055,6 +1055,8 @@ class _PackageBoundObject(object):
                          subfolders use forward slashes as separator.
         :param mode: resource file opening mode, default is 'rb'.
         """
+        if mode == 'rt':
+            mode = 'r'
         if mode not in ("r", "rb"):
             raise ValueError("Resources can only be opened for reading")
         return open(os.path.join(self.root_path, resource), mode)