Generalize longpoll to work for any param-less JSON-RPC call
Generalize longpoll to work for any param-less JSON-RPC call

This enables getmemorypool LP

thrasher-/eloipool,imsaguy/eloipool,thrasher-/eloipool,uingei/eloi,jameshilliard/4tar-eloipool,ahmedbodi/SHA-Eloipool-MMCFE-,svasva/eloipool,uingei/eloipool,wizkid057/eloipool,thrasher-/eloipool,cinnamoncoin/eloipool-1,pointgaming/point-gaming-btc