http://www.mydomain.com/some/subdir/file.php
	
$.post('/some/subdir/file.php', ...);
	
/**
 * Retrieves the current root URL.
 *
 * @return string the root URL
 */
$.fn.rootUrl = function() {
	var url = location.href;
	return url.substring(0, url.indexOf('/', 7));
};