+ reduce memory use in binary GET

Hi,

I noticed that a byte[] array of the size of the content fetched from memcached is created for every GET that is successful, in order to represent a errorMsg. This results in a lot of memory allocations, that are subsequently not used.

This PR (which I originally opened against dustin/java-memcached-client) removes the byte[] allocation in the SUCCESS scenario, removing allocation pressure. The below screen shots are from a JMC view of a flight recorder profile showing the removal of GB's of allocations from a load test that simulates 760,000 gets for 26k of content stored in memcached. Removing the allocations, allowed another 70k of requests to be generated by the load test.

Apologies if the two repositories are the one in the same thing, and for the duplicate pull requests, I'm not sure which git repo own the publishing of the maven artifact (http://search.maven.org/#search%7Cgav%7C1%7Cg%3A%22net.spy%22%20AND%20a%3A%22spymemcached%22)

BEFORE
![screen shot 2014-05-25 at 13 17 19](https://cloud.githubusercontent.com/assets/211070/3101298/cbe2bac2-e630-11e3-959d-5d7d0097e2b8.png)


AFTER
![screen shot 2014-05-25 at 14 05 23](https://cloud.githubusercontent.com/assets/211070/3101299/d623eaec-e630-11e3-8030-11c51507777a.png)

cheers
/dom