shuffling lines in a stream

[BCS]

Reply to Andrei,

> BCS wrote:
> 

>> I don't think there is any way to avoid storing the whole file
>> because for a uniform sort there is a possibility that the last line
>> will come out first.
>> 
> I agree with the last paragraph, but lseeking seems overly
> inefficient. Could you avoid that?
> 
> Andrei
> 

algorithmically, I don't think the lseek will matter, as to I/O and cache 
effects, I'll leave that to someone else.