[Sheepdog] panic in get_nth_node

[Liu Yuan]

On 03/15/2012 11:04 AM, huxinwei wrote:

>   I think I figured out what's wrong this time. So here's an new patch obsolete the previous one.
> Would you help to review it ?
> 
> It can be cases that, in some epoch, sheepdog cannot maintain the required copies of replications.
> When recovering from such epoch, we'd better be conservative and double check.


Ah, yeah, nice catch. The logic looks good to me, if no regression, I'll
merge this fix.

Thanks,
Yuan