Merge from pfmooney/client-pool-events

Fix mcavage/node-ldapjs#162

lib/client/pool.js

@@ -47,7 +47,9 @@ function createPool(options, clientpool) {
       client.on('error', function (err) {
         client.removeAllListeners('connect');
         client.removeAllListeners('connectTimeout');
-        clientpool.emit('error', err);
+        if (clientpool.listeners('error').length) {
+          clientpool.emit('error', err);
+        }
         return callback(err);
       });