String.trim()

Pushes support back to at least IE6.

/**
 * String.prototype.trim() polyfill
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim#Polyfill
 */
if (!String.prototype.trim) {
	String.prototype.trim = function () {
		return this.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, '');
	};
}