Session.IsConnected: use RLock instead of Lock to improve performance
Session.IsConnected: use RLock instead of Lock to improve performance

single inserts go up from ~100 to more than 4000 on my dualcore system.
(100 goroutines concurrently inserting single values in local rethinkdb)

dancannon/gorethink,dancannon/gorethink,GoRethink/gorethink,GoRethink/gorethink,dancannon/gorethink,GoRethink/gorethink