pub fn inspect_batch<F>(&self, mut func: F) -> Collection<G, D, R>
    where F: FnMut(&G::Timestamp, &[(D, G::Timestamp, R)])+'static {
        self.inner
            .inspect_batch(move |time, data| func(time, data))
            .as_collection()
    }
Applies a supplied function to each batch of updates.

This method is analogous to `inspect`, but operates on batches and reveals the timestamp of the
timely dataflow capability associated with the batch of updates. The observed batching depends
on how the system executes, and may vary run to run.

# Examples

```
use differential_dataflow::input::Input;

::timely::example(|scope| {
scope.new_collection_from(1 .. 10).1
.map_in_place(|x| *x *= 2)
.filter(|x| x % 2 == 1)
.inspect_batch(|t,xs| println!("errors @ {:?}: {:?}", t, xs));
});
```
differential-dataflow/src/collection.rs