ISPN-2281 Memcached server to pass flags and version via Metadata

* Added MemcachedMetadata to ship flags and version information.
* Added replace(K, V, Metadata) operation and added tests.
* Fixed bug where ReplaceCommand was not using valueEquivalence to
compare old and new value.
* Created ByteArrayCacheTest to exercise cache operations when
storing byte array key/value instances.
* Added externalizers for all metadata classes.