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 
-        zconn._inv_lock.acquire()
-        try:
-            viewed_state = zconn.viewed_db_state
-        finally:
-            zconn._inv_lock.release()
-        return viewed_state
+        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: