Patches CPython's _weakrefset.py to prevent a spurious TypeError when adding an item to a WeakSet

python_weakset_2.7_add_TypeError_fix.patch

This patches WeakSet.add to prevent it having a spurious error if a weak ref goes away between calling this function and adding it
This is done analogously to the patch in https://github.com/python/cpython/commit/f8de3fea1280d55377d40c6e04b64114f9da2fa6:
  "#10360: catch TypeError in WeakSet.__contains__, just like WeakKeyDictionary does."
See https://bugs.python.org/issue10360 for infomration on that

@@ -83,7 +83,11 @@
     def add(self, item):
         if self._pending_removals:
             self._commit_removals()
-        self.data.add(ref(item, self._remove))
+        try:
+            self.data.add(ref(item, self._remove))
+        except TypeError:
+            #Can't add to the cache if ref doesn't exist
+            pass

     def clear(self):
         if self._pending_removals: