Added containers/variant.hpp, it parses.
Made memcached_protocol_t::read_response_t::result_t be a variant instead of boost::variant.
Made memcached_protocol_t::read_response_t::result_t be explicitly instantiated.
Made most of the other variants in memcached/protocol.hpp be ::variant.
Made memcached/protocol.hpp not use boost::variant directly.
Replaced some boost::variants and explicitly instantiated them.