util: add missing r prefix on some __setattr__ calls

# skip-blame just a pair of r prefixes

Differential Revision: https://phab.mercurial-scm.org/D2560

mercurial/util.py

@@ -509,8 +509,8 b' class fileobjectproxy(object):'
     )
 
     def __init__(self, fh, observer):
-        object.__setattr__(self, '_orig', fh)
-        object.__setattr__(self, '_observer', observer)
+        object.__setattr__(self, r'_orig', fh)
+        object.__setattr__(self, r'_observer', observer)
 
     def __getattribute__(self, name):
         ours = {