__init__(), _version_check(): Backport from ZODB 4

lib/python/BDBStorage/BerkeleyBase.py

@@ -219,6 +219,7 @@ class BerkeleyBase(BaseStorage):
         # procedure
         self._tables = []
         self._setupDBs()
+        self._withtxn(self._version_check)
         # Initialize the object id counter.
         self._init_oid()
         # Set up the checkpointing thread
@@ -238,6 +239,9 @@ class BerkeleyBase(BaseStorage):
             self._autopacker = None
         self.log('ready')
 
+    def _version_check(self, txn):
+        raise NotImplementedError
+
     def _make_autopacker(self, event):
         raise NotImplementedError