Description of problem:
-----------------------
With RHS 3.0 Latest build ( glusterfs-3.6.0.28-1.el6rhs ), when the older clients ( less than RHS 3.0 ) mounts the distribute volume, rebalance operation was prohibited with error message "volume rebalance: vol: failed: Volume vol has one or more connected clients of a version lower than RHS-2.1 update 5. Starting rebalance in this state could lead to data loss.
Please disconnect those clients before attempting this command again."

But when the older client is connected, while rebalance already is in progress,
the client mount is accepted.

Version-Release number of selected component (if applicable):
-------------------------------------------------------------
glusterfs-3.6.0.28-1.el6rhs

How reproducible:
-----------------
Always

Steps to Reproduce:
-------------------
1. With RHS 3.0, create a distribute volume with 2 bricks
2. Start the volume
3. Mount the volumes in RHS 3.0 client and add few files
4. Add more bricks to the volume
5. Perform rebalance
6. While rebalance is in progress, mount the volume from older client less than RHS 3.0

Actual results:
---------------
The mount in older client gets mounted successfully

Expected results:
-----------------
The older client mounting the volume and accessing it, while rebalance is in progress, could lead to data loss