Merge 3.6 (fix python#29519)

Author: ambv

Lib/weakref.py

@@ -106,15 +106,15 @@ def __init__(*args, **kw):
         self, *args = args
         if len(args) > 1:
             raise TypeError('expected at most 1 arguments, got %d' % len(args))
-        def remove(wr, selfref=ref(self)):
+        def remove(wr, selfref=ref(self), _atomic_removal=_remove_dead_weakref):
             self = selfref()
             if self is not None:
                 if self._iterating:
                     self._pending_removals.append(wr.key)
                 else:
                     # Atomic removal is necessary since this function
                     # can be called asynchronously by the GC
-                    _remove_dead_weakref(d, wr.key)
+                    _atomic_removal(d, wr.key)
         self._remove = remove
         # A list of keys to be removed
         self._pending_removals = []