Make arrange_core public (#475)

src/operators/arrange/arrangement.rs

@@ -19,7 +19,7 @@
 
 use timely::dataflow::operators::{Enter, Map};
 use timely::order::PartialOrder;
 use timely::dataflow::{Scope, Stream, StreamCore};
 use timely::dataflow::operators::generic::Operator;
 use timely::dataflow::channels::pact::{ParallelizationContract, Pipeline, Exchange};
 use timely::progress::Timestamp;
@@ -557,14 +557,14 @@
 /// This operator arranges a stream of values into a shared trace, whose contents it maintains.
 /// It uses the supplied parallelization contract to distribute the data, which does not need to
 /// be consistently by key (though this is the most common).
-fn arrange_core<G, P, Tr>(stream: &StreamCore<G, <Tr::Batcher as Batcher>::Input>, pact: P, name: &str) -> Arranged<G, TraceAgent<Tr>>
+pub fn arrange_core<G, P, Tr>(stream: &StreamCore<G, <Tr::Batcher as Batcher>::Input>, pact: P, name: &str) -> Arranged<G, TraceAgent<Tr>>
 where
     G: Scope,
     G::Timestamp: Lattice,
     P: ParallelizationContract<G::Timestamp, <Tr::Batcher as Batcher>::Input>,
     Tr: Trace<Time=G::Timestamp>+'static,
     Tr::Batch: Batch,
     <Tr::Batcher as Batcher>::Input: timely::Container,
 {
     // The `Arrange` operator is tasked with reacting to an advancing input
     // frontier by producing the sequence of batches whose lower and upper