Substream applied to unordered streams

[Georgiy Rakov]

Hello,

it seems that 'limit' and 'substream' methods applied to unordered 
stream return result which seems to be only partially deterministic.
Similar thing is true for 'sorted' method provided stream contains equal 
elements and 'sorted' uses algorithm preserving order.

I think the first point is worth being displayed in spec. The second one 
is conditionally - if 'sorted' uses algorithm preserving order.

Could you please tell if you're agree.

Thanks,
Georgiy.