added pooling support for postgres

lib/dialects/postgres/connector-manager.js

 var Query   = require("./query")
   , Utils   = require("../../utils")
+  , pg  = require("pg")
   , without = function(arr, elem) { return arr.filter(function(e) { return e != elem }) }
 
 module.exports = (function() {
@@ -7,6 +8,12 @@ module.exports = (function() {
     this.sequelize = sequelize
     this.client = null
     this.config = config || {}
+    this.pooling = (this.config.poolCfg != null && this.config.poolCfg.maxConnections > 0)
+    // set pooling parameters if specified
+    if (this.pooling) {
+      pg.defaults.poolSize = this.config.poolCfg.maxConnections
+      pg.defaults.poolIdleTimeout = this.config.poolCfg.maxIdleTime
+    }
     this.disconnectTimeoutId = null
     this.pendingQueries = 0
     this.maxConcurrentQueries = (this.config.maxConcurrentQueries || 50)
@@ -44,12 +51,9 @@ module.exports = (function() {
     this.isConnecting = true
     this.isConnected  = false
 
-    var pg  = require("pg")
-      , uri = this.sequelize.getQueryInterface().QueryGenerator.databaseConnectionUri(this.config)
-
-    this.client = new pg.Client(uri)
+    var uri = this.sequelize.getQueryInterface().QueryGenerator.databaseConnectionUri(this.config)
 
-    this.client.connect(function(err, client) {
+    var connectCallback = function(err, client) {
       self.isConnecting = false
       if (!err && client) {
         client.query("SET TIME ZONE 'UTC'")
@@ -60,7 +64,17 @@ module.exports = (function() {
       } else {
         this.client = null
       }
-    })
+    }
+
+    if (this.pooling) {
+      // acquire client from pool
+      pg.connect(uri, connectCallback)
+
+    } else {
+      //create one-off client
+      this.client = new pg.Client(uri)
+      this.client.connect(connectCallback)
+    }
   }
 
   ConnectorManager.prototype.disconnect = function() {