Fix build break with C++11
Fix build break with C++11

The std::atomics in C++11 don't have a copy constructor so
you need an explicit copy constructor

Change-Id: I833058285c72e4071efa32ddaf12a8f54f7e964f
Reviewed-on: http://review.couchbase.org/34876
Reviewed-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>
Tested-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

daverigby/kv_engine,jimwwalker/ep-engine,sriganes/ep-engine,teligent-ru/ep-engine,owendCB/ep-engine,daverigby/kv_engine,couchbase/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,jimwwalker/ep-engine,membase/ep-engine,membase/ep-engine,hisundar/ep-engine,membase/ep-engine,sriganes/ep-engine,hisundar/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,sriganes/ep-engine,daverigby/kv_engine,hisundar/ep-engine,membase/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,daverigby/kv_engine,owendCB/ep-engine,owendCB/ep-engine,sriganes/ep-engine,hisundar/ep-engine,daverigby/ep-engine,couchbase/ep-engine,owendCB/ep-engine,couchbase/ep-engine,daverigby/ep-engine,daverigby/ep-engine