Ext Date类型数据相减
beginTime : Ext.form.DateField
endTime : Ext.form.DateField
allHour : 两时间相差的小时数

var bTime = Date.parseDate(beginTime,'Y-m-d h:i');
var eTime = Date.parseDate(endTime,'Y-m-d h:i');
var allHour = (eTime - bTime)/(60*60*1000);