MemcacheCommand: handle TCP options in packet parsing.

The data offset field of a TCP header contains the number of words the
header is long (minimum 5).  Previously, this code assumed all TCP
headers were exactly 5 words long and would treat the TCP options as
payload. This patch makes the parser respect the data offset field and
start parsing data at the correct point.
Parse the Memcache Binary Protocol.

This patch replaces ASCII protocol parsing with Binary Protocol parsing
for GetK and GetKQ responses.

https://code.google.com/p/memcached/wiki/MemcacheBinaryProtocol