Fixed syntax error and added historic connection functionality to zconn_at

lib/zodb.py

@@ -180,13 +180,15 @@ def zconn_at(zconn): # -> tid
         raise AssertionError("zconn_at: TODO: add support for zstor %r" % zstor)
 
     elif zmajor == 4:
-        if not zconn.before 
+        if zconn.before is None:
             zconn._inv_lock.acquire()
             try:
                 viewed_state = zconn.viewed_db_state
             finally:
                 zconn._inv_lock.release()
             return viewed_state
+        else:
+            return before2at(zconn.before)
     
     # TODO ZODB3  
     else: