Load only the modules not yet defined or at least try to validate them

I wrote also two tests to check the new features added:
old requirejs (too many requests jQuery lodash and Backbone have already being loaded into the DOM)
http://gianlucaguarini.com/experiments/requirejs/requirejs-test1.html

The new requirejs with my fix loads only the scripts really needed
http://gianlucaguarini.com/experiments/requirejs/requirejs-test3.html