js 去除左右首尾空格
ie6不支持jquery的trim()方法，于是找来这个代码备用

>>> "sss".replace(/^\s+|\s+$/g, "")"sss">>> " sss".replace(/^\s+|\s+$/g, "")"sss">>> " sss ".replace(/^\s+|\s+$/g, "")"sss">>> " s s s ".replace(/^\s+|\s+$/g, "")"s s s"