function getScript(url, callback) {
    	var headEl = fabric.document.getElementsByTagName("head")[0],
    	    scriptEl = fabric.document.createElement('script'), 
    	    loading = true;

    	scriptEl.type = 'text/javascript';
    	scriptEl.setAttribute('runat', 'server');

    	/** @ignore */
    	scriptEl.onload = /** @ignore */ scriptEl.onreadystatechange = function(e) {
    	  if (loading) {
    	    if (typeof this.readyState == 'string' && 
    	        this.readyState !== 'loaded' && 
    	        this.readyState !== 'complete') return;
      	  loading = false;
      		callback(e || fabric.window.event);
      		scriptEl = scriptEl.onload = scriptEl.onreadystatechange = null;
      	}
    	};
    	scriptEl.src = url;
    	headEl.appendChild(scriptEl);
    	// causes issue in Opera
    	// headEl.removeChild(scriptEl);
    }
Inserts a script element with a given url into a document; invokes callback, when that script is finished loading
@method getScript
@memberOf fabric.util
@param {String} url URL of a script to load
@param {Function} callback Callback to execute when script is finished loading