Make memcached.h includable from C++
Make memcached.h includable from C++

Change-Id: Ie10ff9f45a4744ec33248fa08a71715346a7cbe1
Reviewed-on: http://review.couchbase.org/48810
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

daverigby/memcached,daverigby/memcached,owendCB/memcached,couchbase/memcached,owendCB/memcached,couchbase/memcached,owendCB/memcached,cloudrain21/memcached-1,daverigby/memcached,couchbase/memcached,couchbase/memcached,daverigby/kv_engine,cloudrain21/memcached-1,daverigby/kv_engine,daverigby/kv_engine,cloudrain21/memcached-1,cloudrain21/memcached-1,daverigby/memcached,owendCB/memcached,daverigby/kv_engine