add libs has_been_loaded check & yui tests require field "url" support

1. Add libs/sharelib priority check:  lib, common lib > share lib, once lib/common been loaded,then won't load again from share lib to aovid overwrite error

2. For some yui test case,users require a url like http://chaijs.com/chai.js to load some js file before run the tests, they don't want do that in test cases themselves,so in arrow they can define it in  yui test case "require" field , we will resolve that and load them first for the test. thought this is not official supported in YUI, but it will benefit some special case and won't cause any error( YUI will give a module not loaded warning).