Support function-like construction (plus test) (brianc#23)

* Support function-like construction

Remove the necessity of using `new` in front of the `Pool`, i.e. allow it to be used as a regular function. This is following brianc#1077

* add Pool factory test

Author: cody-greene

index.js

@@ -4,6 +4,9 @@ var EventEmitter = require('events').EventEmitter
 var objectAssign = require('object-assign')
 
 var Pool = module.exports = function (options, Client) {
+  if (!(this instanceof Pool)) {
+    return new Pool(options, Client)
+  }
   EventEmitter.call(this)
   this.options = objectAssign({}, options)
   this.log = this.options.log || function () { }

test/index.js

@@ -12,6 +12,12 @@ if (typeof global.Promise === 'undefined') {
 }
 
 describe('pool', function () {
+  it('can be used as a factory function', function () {
+    var pool = Pool()
+    expect(pool instanceof Pool).to.be.ok()
+    expect(typeof pool.connect).to.be('function')
+  })
+
   describe('with callbacks', function () {
     it('works totally unconfigured', function (done) {
       var pool = new Pool()