Add a test to verify wrapping works correctly at maximum buffer size
Remove unnecessary condition from wrapping code path
UnicastThroughputTest: Remove verify_result fn in favour of assert_eq
UnicastThroughputTest: calculate expected value at point of checking

The simple version of the function is so fast that it's not noticeably
slower to do this, and it makes it easier to vary the number of
iterations.
UnicastThroughputTest: run fewer iterations of the pipes benchmark

This reduces the execution time to acceptable levels.
Add a safe, last-leg-only API to move values out of the disruptor

This allows callers to receive values conveniently without having to
make a closure.
Factor out method to access a SingleConsumer's Sequence