Only call client.ref if it exists

* Only call client.ref if it exists. Fixes brianc#2582

* Make test requiring port less flakey

* Bump port range

Fixes brianc#2582
Fixes brianc#2584

Author: brianc

packages/pg-pool/index.js

@@ -137,7 +137,7 @@ class Pool extends EventEmitter {
       const idleItem = this._idle.pop()
       clearTimeout(idleItem.timeoutId)
       const client = idleItem.client
-      client.ref()
+      client.ref && client.ref()
       const idleListener = idleItem.idleListener
 
       return this._acquireClient(client, pendingItem, idleListener, false)

packages/pg/test/integration/client/connection-timeout-tests.js

@@ -7,7 +7,7 @@ const suite = new helper.Suite()
 
 const options = {
   host: 'localhost',
-  port: 54321,
+  port: Math.floor(Math.random() * 2000) + 2000,
   connectionTimeoutMillis: 2000,
   user: 'not',
   database: 'existing',