Deleting the jar of a ghosted Python persistent object shouldn't try to...

Deleting the jar of a ghosted Python persistent object shouldn't try to activate it. This was an error encountered testing ZEO:

```python
File "//Projects/GithubSources/ZEO/src/ZEO/tests/testZEO.py", line 1566, in ZEO.tests.testZEO.gracefully_handle_abort_while_storing_many_blobs
Failed example:
    c.tpc_abort(t)
Exception raised:
    Traceback (most recent call last):
      File "//bin/pypy/lib-python/2.7/doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest ZEO.tests.testZEO.gracefully_handle_abort_while_storing_many_blobs[12]>", line 1, in <module>
        c.tpc_abort(t)
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/ZODB-4.2.0.dev0-py2.7.egg/ZODB/Connection.py", line 754, in tpc_abort
        self._invalidate_creating()
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/ZODB-4.2.0.dev0-py2.7.egg/ZODB/Connection.py", line 775, in _invalidate_creating
        del o._p_jar
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/persistent-4.0.10.dev0-py2.7.egg/persistent/persistence.py", line 287, in __delattr__
        object.__delattr__(self, name)
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/persistent-4.0.10.dev0-py2.7.egg/persistent/persistence.py", line 92, in _del_jar
        self.__setattr__('_Persistent__jar', None)
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/persistent-4.0.10.dev0-py2.7.egg/persistent/persistence.py", line 249, in __getattribute__
        oga(self, '_p_activate')()
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/persistent-4.0.10.dev0-py2.7.egg/persistent/persistence.py", line 358, in _p_activate
        jar.setstate(self)
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/ZODB-4.2.0.dev0-py2.7.egg/ZODB/Connection.py", line 869, in setstate
        self._setstate(obj)
      File "//Projects/VirtualEnvs/ZODBpypy/site-packages/ZODB-4.2.0.dev0-py2.7.egg/ZODB/Connection.py", line 910, in _setstate
        p, serial = self._storage.load(obj._p_oid, '')
      File "//Projects/GithubSources/ZEO/src/ZEO/ClientStorage.py", line 842, in load
        data, tid = self._server.loadEx(oid)
      File "//Projects/GithubSources/ZEO/src/ZEO/ServerStub.py", line 176, in loadEx
        return self.rpc.call("loadEx", oid)
      File "//Projects/GithubSources/ZEO/src/ZEO/zrpc/connection.py", line 781, in call
        raise inst # error raised by server
    POSKeyError: 0x02'')
```

persistent/persistence.py

@@ -85,11 +85,10 @@ class Persistent(object):
 
     def _del_jar(self):
         jar = self.__jar
-        oid = self.__oid
         if jar is not None:
             if self._p_is_in_cache():
                 raise ValueError("can't delete _p_jar of cached object")
-            self.__setattr__('_Persistent__jar', None)
+            _OSA(self, '_Persistent__jar', None)
             _OSA(self, '_Persistent__flags', None)
 
     _p_jar = property(_get_jar, _set_jar, _del_jar)

persistent/tests/test_persistence.py

@@ -112,6 +112,29 @@ class _Persistent_Base(object):
         del inst._p_jar
         self.assertEqual(inst._p_jar, None)
 
+    def test_del_jar_of_inactive_object_that_has_no_state(self):
+        # If an object is ghosted, and we try to delete its
+        # jar, we shouldn't activate the object.
+
+        # Simulate a POSKeyError on _p_activate; this can happen aborting
+        # a transaction using ZEO
+        broken_jar = self._makeBrokenJar()
+        inst = self._makeOne()
+        inst._p_oid = 42
+        inst._p_jar = broken_jar
+
+        # make it inactive
+        if hasattr(inst, '_Persistent__flags'):
+            # Python version
+            inst._Persistent__flags = None
+        else:
+            inst._p_deactivate()
+        self.assertEqual(inst._p_status, "ghost")
+
+        # delete the jar; if we activated the object, the broken
+        # jar would raise NotImplementedError
+        del inst._p_jar
+
     def test_assign_p_jar_w_new_jar(self):
         inst, jar, OID = self._makeOneWithJar()
         new_jar = self._makeJar()