Add missing header (fixes build on OpenBSD).
Add missing header (fixes build on OpenBSD).

Metaswitch/memcached,mrkwse/memcached,abhinavdangeti/memcached,mrkwse/memcached,couchbase/memcached,jimwwalker/memcached,zbase/memcached,abhinavdangeti/memcached,daverigby/memcached,zbase/memcached,cloudrain21/memcached-1,daverigby/kv_engine,daverigby/kv_engine,cloudrain21/memcached-1,Metaswitch/memcached,daverigby/memcached,mrkwse/memcached,daverigby/kv_engine,couchbase/memcached,mrkwse/memcached,Metaswitch/memcached,owendCB/memcached,couchbase/memcached,jimwwalker/memcached,cloudrain21/memcached-1,cloudrain21/memcached-1,daverigby/memcached,Metaswitch/memcached,Metaswitch/memcached,zbase/memcached,owendCB/memcached,daverigby/kv_engine,abhinavdangeti/memcached,owendCB/memcached,jimwwalker/memcached,zbase/memcached,couchbase/memcached,abhinavdangeti/memcached,abhinavdangeti/memcached,daverigby/memcached,zbase/memcached,owendCB/memcached