Encounter order

[Andrey Breslav]

> Ah, 'unordered' is my 'asKindBParallel' operation.  To make my previous discussion concrete, I'm arguing that the result of 'unordered' -- call it an 'UnorderedStream' -- should _not_ extend 'Stream', but rather should have its own set of operations that make sense in an unordered world (e.g., no 'findFirst', no 'skip', commutative-op-only 'reduce', etc.).
But as Brian pointed out, it needs to still have sorted(), groupBy() and 
such, because sometimes we need then stable, and sometimes we need them 
just fast.